$@Sammi78952$

$1$. You are entitled to a special discount___provided that____ in cash.

$-$> provided that : miễn là 

$2$. But ___for the rain___, they would have gone on a picnic.

$-$> Cấu trúc câu đk loại 3

$3$. Take a book to read __in case your flight will be_____delayed.

$-$> in case : trong trường hợp 

=>

1. You are entitled to a special discount provided (that) you pay in cash.

-> provided that ~ miễn là

2. But for the heavy rain, they would have gone on a picnic.

-> but for ~ nếu không

3. Take a book to read in case your flight is delayed.

-> in case: phòng khi, trong trường hợp