P is the sole product made when two volumes of ammonia gas combine with one volume of carbon dioxide gas, with both volumes measured at r.t.p. What is the formula of P?
- A$\text{NH}_2\text{CO}_2\text{NH}_4$
- B$(\text{NH}_2)_2\text{CO}$
- C$\text{NH}_4\text{CO}_2\text{NH}_4$
- D$(\text{NH}_4)_2\text{CO}_3$