In
the sentence: The candidates will be speaking at today's rally.
The
answer is letter A: candidates.
Sentences
naturally contain a subject and a predicate. They could be simple (one independent clause), compound (two
independent clause with coordinating conjunction), complex (a subordinate &
independent clause) and compound-complex sentences (subordinate & two
independent clause). These include clauses, conjunctions, coherence and balance
and even to the number of words you use in your subject and predicate.
In this case, the
subject is candidates
while the predicate is will be speaking at today's rally.