In each question, the first and the last sentences of the passage are numbered S1 and S6 respectively. The rest of the passage is split into four parts. These four sentences are jumbled. Read the sentences and identify their correct and logical order.

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S1: We and all other animals breathe in and breathe out air all the time.
P: If we stop breathing, we die.
Q: It is because of this fact that we are able to live.
R: It is called the atmosphere.
S: All parts of the earth are surrounded by air.
S6: It is a part of the earth.
The Proper sequence should be: