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Hi! Are these all grammatically correct? Do I need an apostrophe? Thanks, Fulvio

1. The reason they moved to the countryside, is it is cheaper.

2. The reason he is late is he slept in.

3. The reason he is unhappy is he broke up with his girlfriend.

4. The reason he is so good at the piano is he practices every day.

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We commonly add 'that'.

Where do you want to put an apostrophe?

1. The reason they moved to the countryside, is (that) it is cheaper. Remove the comma.

2. The reason he is late is (that) he slept in.

3. The reason he is unhappy is (that) he broke up with his girlfriend.

4. The reason he is so good at the piano is (that) he practices every day.