In the following question, there are six sentences marked S1, S6, P, Q, R, and S. The positions of S1 and S6 are fixed. You are required to choose one of the four alternatives which would be the most logical sequence of the sentence in the passage.

S1. Although fruits can no longer grow once picked,

P. taking in oxygen and

Q. they continue to respire for some time,

R. giving off carbon dioxide,

S. just as human beings do

S6. when they breathe.