$1.$ The kids would rather watch cartoons whenever they are allowed.

- S + would rather + V (Bare): Ai đó thà làm gì.

$2.$ He attended the Fruit Festival in Luc Ngan District last week, didn't he?

- Tag question: Phần mệnh đề ở dạng khẳng định thì phần láy đuôi ở dạng phủ định và ngược lại.

$3.$ The weather hasn't been good enough for them to provide food and medicines for the victims of the flood.

- too bad = not good enough (adj.): quá tệ = không đủ tốt.

$-$ S + to be + (not) + adj + enough + (for sb) + to V: đủ/ không đủ để làm gì.

$4.$ I think that your question is a piece of cake.

- very easy (adj.) = a piece of cake (idiom.): dễ ẹt.

$5.$ They couldn't decide where to reach on holiday.

- go on = reach on (v.): đi đến.