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?

Glaciers deposit their sediment when they melt.
When do glaciers deposit their sediment?

Sliding friction is friction that acts on objects when they are sliding over a surface.

What type of friction is friction that acts on objects when they are sliding over a surface?