Which of the following characteristics are typical of external processes ?1. They operate on the surface of the earth.2. They act suddenly.3. They tend to reduce differences in relief.4. They can be observed.

Which of the following characteristics are typical of external process

1.	Which of the following characteristics are typical of external processes ?1. They operate on the surface of the earth.2. They act suddenly.3. They tend to reduce differences in relief.4. They can be observed.
A.	1, 2 and 4
B.	1, 3 and 4
C.	1, 2 and 3
D.	1 and 4
Answer» C. 1, 2 and 3