Directions: Each of the following items in this section consists of a sentence, parts of which have been jumbled. These parts have been labelled as P, Q, R and S. Given below each sentence has four sequences, namely (a), (b), (c) and (d). You are required to re-arrange the jumbled parts of the sentence and mark your response accordingly.

Complex systems that regulate (P) / Temperature, water, and carbon dioxide levels (Q) / Plants are (R) / In the environment (S)