you will read it as a title block
Option C contains a run-on sentence (I would call it a comma splice).
A better way to phrase the sentence could be:
1. A giant clam grows huge; it can weigh hundreds of pounds.
2. A giant clam grows huge. It can weigh hundreds of pounds.
To compete is a nominal infinitive.
Answer:
The answer is A, "What a nice plump mouthful, she will be better to ear than the old woman."
Explanation:
We know this because the wolf eats both the grandmother AND Little Red Riding Hood. The other options do not forshadow anything, since we know that forshadowing it basically giving the reader clues as to what happens later in the story!
Hope this helps!