Me i'm literally gonna cry if i get this wrong

a student adds a suspension of baker's yeast cells into bread dough. when this mixture is left in a large bowl undisturbed for several hours, the student returns to find that the bread dough has doubled in size. what gas molecule is responsible for this increase in dough size?
a. o2
b. n2
c. h2
d. co2

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