One month has passed till now.In this period, the sharks taught the baby whale...

[Volcano1985]

One month has passed till now.In this period, the sharks taught the baby whale the killing methods

The second clause should be present perfect ?

[Alan]

Hi Volcano,

I think I'd like to turn the sentences around to read:

It's a month now since the sharks taught the baby whale how to kill..

Alan
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English as a Second Language
You can read my ESL story Phrasal Verbs/run

[Yankee]

Hi Volcano

Here is another suggestion:

- This past month the sharks taught the baby whale how to kill.

I'd say you could use either the simple past tense or the present perfect in that sentence.
.