The place of already in a sentence

[ElvisFannetjeh]

Is the place that I have put the word already in, correct in this sentence?
They have to be able already to form the irregular past tense.

I always have trouble with putting words like already, always, often,.. on the right place in a sentence.

I hope you can help me?

[Mister Micawber]

Adverbs of time and frequency can go in several places. In this case:

They have to be able already to form the irregular past tense.
They have to be able to form the irregular past tense already.
They have to already be able to form the irregular past tense.
They already have to be able to form the irregular past tense.
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Native English teacher at Mister Micawber's