Which answer best describes the verb tenses in the sentence?
by the time we got to austin, the puppy falls asleep in the back of the van.
a. the verb tenses are consistent.
b. the verb tenses shift.

The answer that best describes the verb tenses in the sentence is B) The verb tenses shift.
In the first part of the sentence, past simple tense is used (got), and in the second part, present simple tense is used (falls). That is why the tenses are inconsistent, they shift.