read the sentence. open his chemistry book, trevor knew he had a long night of studying ahead of him. which…

Brief Explanations:

The present - participle "Opening" is used to show an action that is happening simultaneously with the main action. "To open" is an infinitive and doesn't fit the context of two concurrent actions. "Opened" is past - tense and makes it seem like the book - opening happened before the main thought. "Opens" is present - tense third - person singular and is grammatically incorrect here.

Answer:

Opening