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

[EX Q]: Smaller size of ring will a summer drought cause in a tree.
[EX A]: What size of ring will a summer drought cause in a tree?

[EX Q]: Microscopes were first developed in the early 1600s by eyeglass makers.
[EX A]: Microscopes were first developed in the early 1600s by this trade?

[EX Q]: Because charges must have an unbroken path to follow, electric current cannot flow through a material unless it forms a closed loop.
[EX A]:
Because charges must have an unbroken path to follow, electric current cannot flow through a material unless it forms what?