Read the sentence:

"Gregor watched, assessing how Sasha reacted to his news."

Which statement best explains how the underlined clause conveys meaning?

A. It is an adverbial clause explaining Sasha's behavior.
B. It is a noun clause indicating what Gregor was observing.
C. It is a noun clause describing what Sasha was responding to.
D. It is a relative clause specifying the information Gregor gave Sasha.