Answer:
B. Insects exist in the millions in the taiga during the summer because of the growth of trees.
Step-by-step explanation:
A is wrong because not all birds from every single biome migrate to eat those insects. C is wrong because birds CAN exist in the taiga during winter, but these specific birds migrate for the insects. D can be seen as correct, but it is wrong because it says MANY animals, when really the paragraph is stating that these birds migrate. D would've been correct if it said "During the summmer, these birds mirgrate to the Taiga because of the large food sources."
I also just took the quiz and D was incorrect, haha.