In the question , some parts of the sentences have errors and some have none. Find out which part of a sentence has an error .The number of that part is the answer. If there is no error, then your answer is (4) i.e. No error.
Some categorically suspected (1)/having seen the (2)/gaurd and thief together. (3)/No error(4)

Answer

1

Explanation

Here, Some were surprised/Some categorically denied ....... should be used.