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

Q: The human body has as many as two trillion lymphocytes, and lymphocytes make up about 25% of all of leukocytes.

A: The human body has as many as two trillion lymphocytes, and lymphocytes make up about 25% of all of what?
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Q: You call materials that have high resistance to electric current electric insulators.

A: What do you call materials that have high resistance to electric current?
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Q: The logistics of carrying out cellular metabolism sets limits on the size of the cell.

A:
The logistics of carrying out cellular metabolism sets limits on what physical property of the cell?
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