The first and sixth sentences of a passage are given in the beginning and in the end, respectively. The middle four sentences have been jumbled up. These are labelled as P, Q, R and *. Find out the proper order for the four sentences.
S1: As the pressure on land rises, more and more marginal areas in the world are being used for agriculture.
P: While irrigation may be the most obvious response to drought, it has proved costly and can only benefit a fortunate few.
Q: Much of this land is located in the arid or semi-arid belts where rain falls irregularly and much of the precious water is soon lost as surface runoff.
R: There is now increasing interest in a low cost alternative - generally referred to as "water harvesting".
*: Recent droughts have highlighted the risks to human beings and livestock, which occur when rains falter or fail.
S6: Water harvesting is the collection of runoff for productive purposes.
The proper sequence should be
A. QRSP
B. PSQR
C. QSPR
D. RPSQ
