Small sailboats can easily turn over in the water ______ they are not managed carefully.
| A．though | B．before | C．until | D．if |
— It’s no easy task to catch a ticket on a website that receives 1 billion clicks daily.
—I can’t agree with you more. There ________ be errors for every single step.
| A．should | B．must | C．will | D．can |
—I wonder what makes you a successful manager.
—I ________ as a waiter for five years，which contributes a lot to my today’s work.
| A．serve | B．have served | C．had served | D．served |
----What’s that noise?
---- There’s a truck stopping outside．It’s someone something.
| A．deliver | B．to deliver | C．delivering | D．delivered |
After the trainer was sure that the whale could look after itself, he _______ it into the sea.
| A．transported | B．delivered | C．released | D．handled |
The course about Chinese food attracts over 100 students per year, _______ up to half are from overseas.
| A．in which | B．of whom | C．with which | D．for whom |