[Help!] Revise this sentence correcting any vague and ambiguous pronouns? Make sure all antecedents are clear?

6. The whales seem to migrate during the night, which takes a great deal of energy.

> "which" is too vague because it is trying to refer to the entire previous clause.

Suggestion:

The whales use a great deal of energy to migrate during the night.

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7. If you study whales, you must have patience.

> This use of the word "you" is inappropriate for formal writing or speech.

Suggestion:

Studying whales requires patience.

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8.Sometimes the whales will not come to the surface for long periods of time, and this can be frustrating.

> The word "this" does not have a proper antecedent. It is trying to refer to the entire previous clause.

Suggestion:

It is sometimes frustrating when the whales will not come to the surface for long periods of time.

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9. When the whales do surface, they often raise their tail flukes as they dive down again. That is a beautiful sight.

> The word "that" does not have a proper antecedent. It is trying to refer to the entire preceding sentence.

Suggestion:

It is a beautiful sight to see the whales surface, then raise their tail flukes as they dive down again.

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10. Many whales use their voices to communicate, which we refer to as songs.

> The word "which" has no antecedent.

Suggestion:

To communicate, many whales use their voices to produce what we call songs.