B. atmosphere since the atmosphere is made up of o2, co2 (a greenhouse gas) and nitrogen. those are the primary elements
<span>Earth rotates around its axis and also revolves around the Sun. Rotation is the motion that causes day and night. Earth completes one full rotation every 24 hours. The part of the Earth that faces the Sun has day and the other part has night.</span>
I think it is A. they can start to hear sounds at 20 weeks
