Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

[EX Q]: The human body has as many as two trillion lymphocytes, and lymphocytes make up about 25% of all of leukocytes.
[EX A]: The human body has as many as two trillion lymphocytes, and lymphocytes make up about 25% of all of what?

[EX Q]: The long, threadlike extensions of the nerve cell help transmit nerve impulses.
[EX A]: Which part of the nerve cell helps transmit nerve impulses?

[EX Q]: Physical and chemical differences help ecologists distinguish between freshwater and marine types of biomes.
[EX A]:
Physical and chemical differences help ecologists distinguish between freshwater and marine types of what?