Rearrange the parts of the sentence in correct order.

Birds' heart, lungs and

P. uptake and intensive exertion compared

Q. to humans, which enables them to function

R. efficiently at these very high altitudes

S. muscles are more efficient for oxygen

SPQR

The correct answer is Option (3) → SPQR

Birds' heart, lungs and
S. muscles are more efficient for oxygen
P. uptake and intensive exertion compared
Q. to humans, which enables them to function
R. efficiently at these very high altitudes