During reading, if a student is piercing information together as they read a text keeping track of what is happening, he/she is—

Synthesizing while reading means combining/piecing together various pieces of information from the text to build comprehensive understanding while keeping track of what is happening. Inferring is deriving conclusions not directly stated. Skimming is rapid reading for the gist. Paraphrasing is restating in one's own words. The description in the question—piecing information together while tracking events—precisely matches synthesizing. Hence (4) is correct.