The co2 level is during winter in the northern hemisphere compared to levels in the summer. the same higher lower

I believe that the level of CO2 level is higher during winter in the northern hemisphere compared to levels in the summer. There's more carbon dioxide in the winter and a bit less in the summer. That's the collective breathing of all the plants in the Northern Hemisphere. Plants are accumulating carbon in the spring and summer when they are active, and they are releasing carbon back to the air in the fall and winter. 

The best answer is A - body plan.

Hox genes also called homeotic genes are any group of genes which control the pattern of body formation in the early stages of embryonic development of organisms.

These genes code for a what are known as transcription factors that direct cells to form various parts of the body.

A homeotic  protein has the ability to activate one gene but repress the other, producing effects which complement the development of organism.

Human have 39  hox genes divided into four separate clusters  A, b, C, D, located on different chromosomes.