1. past
2. had, past perfect
3. has, have, present perfect
4. future
5. present
6. will have, future perfect
and #6 at the bottom is had cleared
I would say that sometimes you would not 'identify' a mistake in your head. Also if you read it out loud you might realize how it does not make sense in your sentence.
Hope this helped!
;D
Answer: a. what the author was trying to achieve
Explanation: It's either this one of d. because what the author was trying to achieve is what the authors purpose for writing the work is and an authors work should accomplish or close to accomplish their purpose.
