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. 

The air is cold. Water is in the air. The water forms tiny ice crystals. The ice crystals collide with each other. The ice crystals stick to each other. The ice crystals get bigger as more of them stick together. The ice crystals get too heavy to be in the air. The ice crystals become snowflakes. The snow flakes fall to the ground as snow. 
How does snow form?

Algae and plankton die. The dead algae and plankton end up part of sediment on a seafloor. The sediment breaks down. The bottom layers of sediment become compacted by pressure. Higher pressure causes the sediment to heat up. The heat causes chemical processes. The material becomes a liquid. Is known as oil. Oil moves up through rock. 
How does oil form?

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. 

How do muscles work?