Directions: In the following sentence, three substitutions are given for each italicised part. If one of them is better than the italicised part, that should be your answer. If none of the substitution improves the sentence, the answer should be (4).

I know he's a cheat and a liar, I studied the behaviour of criminals all my life.

'Have studied' is correct because it links the lifelong experience to the present moment when the speaker says 'I know he's a cheat'. Present perfect tense shows action continuing from past to present. 'Studied' (simple past) would imply the studying is completely finished and disconnected from the present knowledge, which doesn't fit the context.