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$\text{4. The students will take part in the "Green Day" activities. They are very keen}$

$\rightarrow$ $\text{They're very keen on taking part in the "Green Day" activities.}$

$\text{Cấu trúc keen on:}$

$\text{S+keen(s) on+V-ing+O=Ai đó thích thú làm việc gì đó}$

$\text{5. You should develop habits that will keep your body healthy and clean. It's necessary}$

$\rightarrow$ $\text{It's necessary for you to develop habits that will keep ...}$

$\text{Cấu trúc với tobe+necessary:}$

$\text{S+tobe+necessary+(for sb)+to do something+O=Cần thiết để làm gì đó}$

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