Complete the starship captain's final log entry about a bizarre alien encounter by choosing the correct word for each blank.

The crew eventually realized that what baffled them most was how the creatures effortlessly manipulated whatever matter they happened to touch.

The crew eventually realized that what baffled them most was how the creatures effortlessly manipulated whatever matter they happened to touch.

what is a nominal relative pronoun meaning "the thing that." It acts as the subject of the verb "baffled." Using "that" would create an incomplete noun clause lacking a subject, and "which" requires a preceding noun (antecedent).

how acts as a nominal relative word meaning "the way in which." The entire clause functions as the subject complement after the verb "was."

whatever acts as a determinative in this nominal relative clause, meaning "any matter that." "Whichever" would imply a specific, limited selection of matter, whereas "whatever" correctly implies an open, limitless possibility.