The first and sixth sentences are given as S1 and S6. The middle four sentences in each have been jumbled up and labelled as P, Q, R and S. You are required to find the proper sequence of the four sentences and mark your response accordingly.   

S1: Air pollution is a rising concern in today’s society and environment.

P: Additionally, the Montreal Protocol is an international agreement to protect the ozone layer from deteriorating chemicals.

Q: This pollution can lead to negative effects on humans, the environment, and all living things on Earth.

R: The negative effects of air pollution can lead to the deterioration of the ozone layer.

S: It is caused by the pollution of chemicals produced by human factors, industries, cars, etc.

S6: it has been signed by 197 countries to protect the ozone layer.