Wemust______thattheexperimentiscontrolledasrigidlyaspossible.
A、assureWeregretto________thatitmaynotbepossibletodealwitheveryrequest.
________theconcerthadbegundidwerealizewhatasplendidshowitwasgoingtobe.
I'msorryIforgottowrite;Ihadsomuchelse________mymind.
It________asashocktorealizethatIwasnotaloneintheroom.
Tostudyaforeignlanguage,__________.
