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

Input: Consider Input: The active transport of ions across the membrane causes an electrical gradient to build up across the plasma membrane.

Output: The active transport of ions across the membrane causes an electrical gradient to build up across the what?


Input: Consider Input: Water plus other substances makes a(n) solution.

Output: Water plus other substances makes what?


Input: Consider Input: When magma reaches the surface through cracks in the earth's crust, a volcanic eruption occurs.
Output: When magma reaches the surface through cracks in the earth's crust, what occurs?