The principal constituent of the atmosphere of the Earth is?

1. The principal constituent of the atmosphere of the Earth is? 

A. Oxygen
B. Carbon
C. Hydrogen

D. Nitrogen

2. What is Dry Ice? 

A. Solid Oxygen

B. Solid Carbon Dioxide

C. Solid Hydrogen
D. Solid Nitrogen

3. What are the primary colours? 

A. White, Black, Blue
B. Red, Yellow, Blue
C. Red, Orange, Blue

D. Red, Green, Blue