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]: Carbon dioxide from the air passes through small pores (holes) in the leaves. These pores are called stomata. Water is absorbed by the roots. It passes through vessels in the stem on its way to the leaves. Sunlight is absorbed by a green chemical in the leaves. 
[A]: What happens during photosynthesis?


[Q]: Fuel is converted to energy when air and petrol mix. The car engine burns the mix of air and petrol. Hot gas from the burning pushes the pistons. The resulting energy powers the crankshaft. Crankshaft powers the gears. The gears make the wheels roll. 
[A]: Describe how a car works


[Q]: When water freezes it becomes 10% bigger, or takes up 10% more space. As water expands it puts great pressure on the walls of anything containing it, including any rocks which happen to be surrounding it. The force of the pressure exerted on the rock surrounding it is enough to wedge the walls of the crack farther apart, thus expanding and deepening the crack. Clay expends when wet like ice does. This causes rock to break apart. Some plants like mosses and lichens are capable of growing without soil on bare rock. When they do this their roots penetrate pores and crevices and cause rocks to split apart as the roots force their way down through the rocks. 
[A]:
How does weathering cause rocks to break apart?