instruction:
In this task, you are given a paragraph, and your task is to construct a question from the given passage. Construct question in such a way that (i) it is well explained in the paragraph, (ii) the words may/may not be present in the paragraph, (iii) it should start with what/how/describe. Avoid creating a question that (i) is just relevant to one or two sentences, and (ii) not relevant to passage. 
question:
Bacteria enters the body. Bloodstream. Cells in the body are attacked. Cells are killed. Different kinds of sickness are formed. 
answer:
How does a virus cause disease?


question:
Electrical signals in the brain travel through nerves to muscles. Two types of proteins exist in filaments in the muscles. The filaments move when the brain instructs them to. The motion of the filaments cause the muscle to shorten and contract. Opposing pairs of muscles exist in order to provide the necessary range of motion. 
answer:
How do muscles work?


question:
Magma rises to the surface during a volcano. The magma undergoes changes in temperature. The magma undergoes changes in pressure. The magma cools. The magma solidifies. The magma crystallizes. Igneous rock is formed. 
answer:

How does igneous rock form?