For formation of frost, there should be 1. Clear sky 2. Calm air 3. Low relative humidity 4. Temperature below freezing point

For formation of frost, there should be 1. Clear sky 2. Calm air 3. Lo

1.	For formation of frost, there should be 1. Clear sky 2. Calm air 3. Low relative humidity 4. Temperature below freezing point
A.	1, 2 and 3
B.	1, 2 and 4
C.	2, 3 and 4
D.	1, 3 and 4
Answer» C. 2, 3 and 4