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

[EX Q]: Bacteria may divide several times an hour.
[EX A]: Bacteria may divide several what an hour?

[EX Q]: Tight junction is the term for a watertight seal between two adjacent animal cells.
[EX A]: What is the term for a watertight seal between two adjacent animal cells?

[EX Q]: Skeletal muscles must work in pairs to move bones back and forth at a joint because they can only contract.
[EX A]:
Skeletal muscles must work in pairs to move bones back and forth at a joint because they can only do what?