Carbon monoxide levels in the atmosphere grew by enough of an increased percentage during the twentieth century that it began to trap heat radiating from the Earth, and it caused the average surface temperature to rise.

Carbon monoxide levels in the atmosphere grew by enough of an increased percentage during the twentieth century that it began to trap heat radiating from the Earth, and it caused the average surface temperature to rise.

Carbon monoxide levels in the atmosphere increased by enough of a percentage during the twentieth century that they began to trap heat radiating from the Earth, causing the average surface temperature to rise.

Levels of atmospheric carbon monoxide increased sufficiently during the twentieth century to begin trapping heat radiating from the Earth, causing the average surface temperature to rise.

Atmospheric carbon monoxide levels increased by a sufficient percentage during the twentieth century to begin trapping heat radiating from the Earth, which caused the average surface temperature to rise.

Levels of carbon monoxide in the atmosphere during the twentieth century increased enough to begin trapping heat radiating from the Earth, causing the average surface temperature to rise.

I said E, but OA is C. The Manhattan explanation states that E changes the meaning of the sentence, but I do not understand. Can you elaborate?

See below for what I feel is incorrect. I would explain E because that is the one we are having problems with.

Carbon monoxide levels in the atmosphere increased by enough of a percentage during the twentieth century that they began to trap heat radiating from the Earth, causing the average surface temperature to rise.

Levels of atmospheric carbon monoxide increased sufficiently during the twentieth century to begin trapping heat radiating from the Earth, causing the average surface temperature to rise.

Atmospheric carbon monoxide levels increased by a sufficient percentage during the twentieth century to begin trapping heat radiating from the Earth, which caused the average surface temperature to rise.

Levels of carbon monoxide in the atmosphere during the twentieth century increased enough to begin trapping heat radiating from the Earth, causing the average surface temperature to rise.

E implies that there is a level of CO in the atmosphere. E.g. the atmosphere is composed of say 100 levels. CO was on level 10 to 15 initially and now it is in level (say) 30-25, resulting in.....
Basically it is not the increase in level, but the increase in amount of CO and we need a quantitative description like % or number to enforce the right meaning.

In choice E (above), "during the twentieth century" describes "levels of carbon monoxide." In the original sentence, "during the twentieth century" describes when the growth occurred.

Rey