In humans,urea is mainly produced in:

Which of the following waste products are removed from the blood during the Ornithine cycle?

In ureotelic animals,urea is formed by

Ketone bodies are produced in the . . . . . . .

The characteristic that is shared by urea,uric acid and ammonia is/are:
$(A)$ They are nitrogenous wastes.
$(B)$ They all need very large amount of water for excretion.
$(C)$ They all are equally toxic.
$(D)$ They are produced in the kidneys.

Frog is