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. 

[Q]: Muscles work by expanding and contracting. A muscle fiber gets a signal from its nerve. Proteins and chemicals release energy to either contract the muscle or relax it. When the muscles contracts the bones connected to he muscle are pulled closer together. When the muscle relaxes the bones move farther apart. 
[A]: How do muscles work?


[Q]: The flu virus has receptors, which are like viral Velcro, on the surface of the virus particle. The receptors will lock onto a target cell using these chemical receptors on the surface, which docks onto the cell surface. The receptors  then go into the cell. The receptors use it like a factory. The receptors take it over and make it produce thousands or in some cases millions of copies of new viruses. The copies come streaming out of the cell. The copies infect other cells to make more viruses, or they escape from the body and infect a new victim. 
[A]: How does a virus cause disease?


[Q]: Grass and small plants grow in an area. These plants die. The soil gains organic material. The soil becomes more fertile. Larger plants are able to be supported. Trees eventually grow. 
[A]:
How do forests form?