1. Magnitude means size. It also means volume, intensity, vastness. In this case, another possible option would be "effect", but it is inaccurate because we don't really see the effect in this sentence. It is theoretically possible to have a huge tornado in a wasteland, with no effect at all.
2. Epicenter means point of earth directly above the earthquake's focus. The focus is also known as hypocenter - the exact underground point where the quake happens. Therefore, epicenter can't be the original source. It is just the point on earth that the earthquake affects the worst.
3. The correct option is The scientific name for chocolate is Theobrina cacao. It is the only option that has a subject and a predicate, two necessary preconditions for a sentence to exist. The first two examples lack predicates, while the last one lacks a subject.
4. You're right, the correct option is Kelley studies the effects of the chemicals in chocolate. The first option lacks a predicate, the third lacks both a subject and a predicate, and the last one lacks a subject.
5. You are right, the correct option is You can grow them with artificial lightning. A verb phrase has two definitions: 1) it is a whole unit in a sentence and it may include the object as well; 2) it is composed of verbs only (main, auxiliary, or modal). Your examples demonstrate the first view, and in that case, we have a phrase "can grow" with a modal, semantically incomplete verb "can" and the main verb "grow".
6. This is a tricky one. I believe the correct answer is Too much light will actually harm the plants. The verb phrase is "will harm" (will - auxiliary, harm - main verb). The option you chose looks like it might be the right one, but it isn't because those are actually two predicates - "makes" refers to "it", while "turn" refers to "leaves". Basically, it does something so that the leaves turn pale.
7. The answer is actually Bud Abbott and Lou Costello. A subject tells us WHO does or is something. The first option refers to the time when something happened (adverbial function), the third option refers to the place where something happened (also adverbial function).
8. Yes, the answer is delighted. It is part of the compound predicate "amused and delighted". A compound predicate is composed of two or more verbs that are independent of each other, but both (or all) are needed to describe the action of the subject.
9. You are right, the fragment is Even on weekends, holidays, and vacations. It is a fragment and not a sentence because it doesn't have a predicate and a subject. Of course, we can deduce from the previous sentence that the parents (subject) gave (predicate) me (indirect object) a curfew (direct object) even on weekends, holidays, and vacations (adverbial phrase). But the fragment can't stand on its own.
10. The answer is If he passes the written test and the road test. This fragment could work only as a dependent (subordinate) clause, within a complex sentence (imagine it attached to the previous option and you'll get the idea). Such as it is, it is the only option that can't stand on its own.
11. I believe the correct answer here is none. A direct object would be a noun phrase that tells us who or what is the recipient of the subject's action. Here, we have no recipients whatsoever.
12. The direct object here is ball. It is the recipient of the subject's action. The subject here is "players" (who does the action), the direct object is "ball" (who or what receives or suffers the subject's action), and "teammates" are an indirect object (affected by the subject's action, but not the direct recipient).
13. The correct answer is a subject. "You" is the WHO of the sentence in this case, even if the sentence is interrogative. It can't be a predicate (as predicates are basically verbs that depict an action), nor an indirect object (read the previous answer to see what an indirect object is).
14. The answer is direct object. It tells us who or what is the recipient of the subject's ("U.S. citizens") action. It provides an answer to the question WHOM (Whom did the U.S. citizens elect?)
15. "Were elected" is a predicate. It tells us about the subject's action. In this case, it is passive voice, so the subject and the object changed their places (presidents are those who usually receive the action of being elected, but in this case they are the sentence's grammatical subject).
16. "Office" is actually none of the above. "In office" would be a noun phrase with an adjective function (referring to "terms" and describing what kind of terms). It can't be a predicate (it is not a verb or a part of a verb phrase), direct object (it is not the recipient), or indirect object (it is not an indirect recipient).
17. "Him" is an indirect object. It tells us TO WHOM the citizens would have given their vote ("the citizens" being the subject, and "their vote" being the direct object, a person or a thing that receives the subject's action). It can't be the predicate because it is not a verb.
