17. Which of the following adds / add nitrogen to the soil?
1. Excretion of urea by animals
2. Burning of coal by man
3. Death of vegetation
 

Select the correct answer using the codes given below.

1. 1 only

2. 2 and 3 only

3. 1 and 3 only

4. 1, 2 and 3

Correct Answer :

1 and 3 only