Question

15) The atrio-ventricular
valves :
a) have three cusps for each
valve
b) their closure is initiated
when the ventricular
pressure exceeds atrial
pressure
c) open by contraction of
papillary muscles .
d) none of the above.​

Answer 1

Explanation:

An ecosystem is a geographic area where plants, animals, and other organisms, as well as weather and landscape, work together to form a bubble of life. Ecosystems contain biotic or living, parts, as well as abiotic factors, or nonliving parts. Biotic factors include plants, animals, and other organisms.

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Answer 2

answer is

d none of the above