What causes heart ventricles to fill with blood?

i. atrial contraction

ii. closing of atrioventricular valves

iii. opening of semilunar valves

a. i only

b. i and ii only

c. ii and iii only

d. iii only

How do accessory pigments chlorophyll?

Nasa scientists must work together to make sure that everything is correct and accounted for when launching a shuttle. besides a physicist, what other type of scientist would be in making sure that the shuttle has the appropriate type and amount of fuel to reach its destination?

What processes take place before the mature mrna exits the nucleus?