The school principal himself ________ a prize in English to the best student at the opening ceremony.

(2014·山西省六所重点中学模拟)—Believe it or not，my sister and I are twins.—Oh，you must have had the case________you were taken for your sister.

___ help, one says "Thankyou" while when _____ help, one asks "Can I help you"

I don’t think you can finish the work ____my help.

E-mail is very popular today. Peopleseldom write letters now,_______