3.Children/ must/ not be/leave alone/ car. A.Children mustn't to be left alone in a car. B.Children mustn't be left alone in a car. C.Children mustn't being left alone in a car. D.Children mustn't be leave alone in a car. 4.Tipping / not/ custom/Viet Nam/ so / you / not/need / tip/if/ don't want. A.Tipping is not a custom in Viet Nam, so you don't need tipping if you don't want to B.Tipping is not a custom in Viet Nam, so you didn't need to tip if you don't want to C.Tipping is not a custom in Viet Nam, so you don't need to tip if you don't want to. D.Tipping is not a custom in Viet Nam, so you don't need tip if you don't want to