In the following questions, some of the sentences have errors and some are correct. Find out which part of a sentence has an error. The number of that part is your answer. If a sentence is free from errors, then your answer is (4) i.e. No error.
We have discussing (1) / all the known mechanisms (2) / of physical growth, (3) / No error. (4)

Answer

A

Explanation

Here, We discussed/ We have been/are discussing should be used. It will be better to use Simple Past