Answer:
A. the squirrel darted down the tree, across the garden, and straight at my crocus bulbs
Explanation:
In simple words, parallelism refers to maintaining similarity among a string of particular category of word types.
In this case, there is a string of adverbs: down.... across.... straight...
The string could be verbs: darted, scurried, skipped
It could be adjectives, gerunds, infinitives, etc.....
