9. Make sure you book tickets _______ because it costs more at the airport! a. by chance b. at a price c. in advance d. for a start

`9.C`

`->` in advance: sớm

`->` đặt sớm vì sẽ giá cao nếu mua ở sân bay

`->` because `+` clause chỉ nguyên nhân

`->` thì HTĐ: S + V-(s/es) + ...

$chucbanhoctot$
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