Sentence Correction (SC) | Re: According to scientists who monitored its path, an expanding cloud

This is a case of cause and effect.

We need -ing modifiers and not -ed modifiers (past participles show intention but in this case, brightening and knocking are not intentional)

A. Brightened - wrong
B. Brightened - wrong
D. Brightened - wrong
E. Knocked - wrong

---