Answer:
7. Mother has been busy cooking for the guests who are arriving in the evening.
You would use "has been", for the sentence implies that it is not the evening yet, which implies it is occurring here and now, necessitating the usage of the present-tense.
8. As I opened my eyes, I saw a strange sight.
This is a "look-back", and so you would use past-tense terms.
9. The sparrow flew away happily after eating the mango.
The sparrow already ate the mango, hence the "after". You would use the past-tense term of flew.
10. In spite of being intelligent, he has not score good marks.
The score is past-tense, for it says "In spite", which means that whatever the event that occurred, it is in the past.
11. The erring students were let off with a strict warning by the principal.
This implies that the warning was already given, so the phrase would be past-tense.
12. Penguins are different from other birds because they have adapted to life in the water.
Again, past tense, because they have already adapted a long time ago, and it was not discovered recently in the present.
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