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

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

The metallic bond is responsible for the properties of metals.
What is responsible for the properties of metals?

We call the solid form of hydrocarbons coal.
What do we call the solid form of hydrocarbons?