The answer is xylem
Explanation
Xylem transports and stores water and water-soluble nutrients in vascular plants. Phloem is responsible for transporting sugars, proteins, and other organic molecules in plants. Vascular plants are able to grow higher than other plants due to the rigidity of xylem cells, which support the plant.
B. The two groups share a relatively recent common ancestor.
(A. Cannot be true because human and monkeys are not that closely related
C. Cannot be true because it is not explicitly indicated by the DNA evidence provided by the excerpt
D. Cannot be true because monkeys would be extinct if human replaced them)
True an increase in birth rate will tend to cause the population