Why Is It Fairly Easy, Out of Context, to Mistake

Multiple Choice

Why is it fairly easy, out of context, to mistake the spoken sentence "The sky is falling" for the sentence "This guy is falling"?

A) They contain the same morphemes, but in different orders.
B) They contain ambiguous or vague referents.
C) The speech stream rarely contains silences between words.
D) There are only about 40 phonemes used in English, not enough to distinguish between sentences that sound the same.