Which is of the following statements about carbon dioxide is TRUE?
A. It is the most potent greenhouse gas.
B. It has not been above 300 ppm in the past 800,000 years.
C. It has recently increased at a rate similar to other periods in history.
D. It is the most abundant greenhouse gas.

Once an egg cell is fertilized by sperm, the cell then, as the embryo develops, it receives nourishment and eliminates wastes by transferring substances from its blood to its mother's blood. a. becomes a fetus immediately and exits the womb b. begins to divide and implants itself in the wall of the uterus c. remains in the uterus without dividing for several months d. travels back to the ovaries until the fetus is developed