Answer:
Correct Option is c) The envelope, which had no return address, was yet sitting on the table at the foot of the staircase.
Explanation:
This sentence is punctuated correctly because comma shows the very little pause between two or more words and at the end of the sentence the full stop implies that sentence is completed.
The answer is C)The envelope, which had no return address, was yet sitting on the table at the foot of the staircase.