Given a scientific passage and an answer, generate a question for the given answer.

Passage: The combined gas law relates pressure, volume, and temperature of a gas. Answer: combines gas law
Which law relates the pressure, volume, and temperature of a gas?

Passage: Like a blanket on a sleeping person, greenhouse gases act as insulation for the planet. The warming of the atmosphere is because of insulation by greenhouse gases. Greenhouse gases are the component of the atmosphere that moderate Earth's temperatures. Answer: insulation
Like a blanket on a sleeping person, greenhouse gases act as what for the planet?

Passage: Figure 2.22 When carbon forms single bonds with other atoms, the shape is tetrahedral. When two carbon atoms form a double bond, the shape is planar, or flat. Single bonds, like those found in ethane, are able to rotate. Double bonds, like those found in ethene cannot rotate, so the atoms on either side are locked in place. Answer: carbon
When what common element forms single bonds with other atoms, the shape is tetrahedral, and when its atoms form a double bond, the shape is planar?