Some researchers believe that there is no doubt ____ a cure for AIDS will be found.

No regular advertiser dare produce anything that fails to stick to the _______ of his advertisement.

_______ have you been here? —I have been here for moths. [ ]

Simon, don’t give up easily. It’s ______________ to lose the chance. –Thanks. Your suggestions are ___________.

Have you ever been to ______ aquarium in Qingdao before?