SENTENCE 1- The first sentence should always introduce the subject of the sentence, to the readers. Sentence Q PROVIDES an insight to the readers about the subject that happens to be causes of global warming. No other sentence provides an introduction rather they elaborate and continue the point raised in Q.Sentence 2- The second sentence is P in the sequence as it is the continuation of sentence Q. When sentence Q began by stating that there are MANY causes of global warming, sentence P continues the discussion by naming one such cause.Sentence 3- Sentence S is an explanation to how HUMANS are a major cause of global warming, a point that was raised in sentence P. Therefore it serves as a continuation to sentence P and is next in the sequence.Sentence 4- Sentence R explains another human activity that is responsible for global warming and is a continuation to sentence S.Hence, the correct order is QPSR and the correct answer is OPTION 1.