Which of the following statements is/are correct? [NDA/NA 2013-I] 1. Air close to the Earth's surface is heavier 2. Air close to the Earth's surface contains large quantity of water vapour and dust particles. Select the correct answer using the code given below:

• A.  1 only
• B.  2 only
• C.  Both 1 and 2
• D.  Neither 1 nor 2