*will mark brainliest to first correct answer* photosynthesis led to increasing levels during the later proterozoic eon? a. oxygen b. water c. carbon dioxide d. none of the above

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