Postsecondary Education Readiness Test (PERT) Practice Test

The selected answer completes the sentence correctly by using the past tense of the verb "to know." The context of the sentence indicates that the action took place in the past, specifically referring to the time before the tunnel was mapped. This means that only a few people had the knowledge of the tunnel's location before it was revealed.

In contrast, other options do not fit as well due to their tense. "Know" implies a present understanding, which does not align with the past context of the sentence. "Have known" suggests a continuous action up to the present, which does not match the timeline given. "Will know" indicates a future understanding, which is irrelevant since the sentence refers to knowledge in a past situation. The past tense "knew" is the most appropriate choice, as it reflects the knowledge that existed prior to the mapping of the tunnel.