like: thì sao → →
if so, why didn’t you tell me beforehand? ☊ 
nếu thế thì sao anh không bảo tôi trước? ☊ I'm not going. How about you? ☊ how about...? ☊
So what if he was late. Who cares? ☊ if ☊
Yes, I was at home on Sunday. What about it? (= Why do you ask?) ☊ it ☊
What about dinner at my place? ☊ place ☊
suppose sb/sth (to be/have) sth: suppose sb/sth + adj./noun: Suppose him (to be) dead—what then? ☊ suppose ☊
What about a trip to France? ☊ what about...? ☊
What if the train is late? ☊ what if...? ☊