The country's railway system has launched online ticket-booking and a real-name ticket purchasing system, and _______ requires passengers to provide their ID numbers when buying tickets.
| A．which | B．that | C．what | D．this |
By looking at a problem in as many ways as possible, creative thinkers can find solutions that would ___ remain invisible.
| A．otherwise | B．yet | C．already | D．forever |
It was foolish of you to take a taxi ___ you could easily walk there in five minutes.
| A．while | B．when | C．since | D．before |
He is only too ready to help others, seldom, ____ refusing them when they turn to him.
| A．if never | B．if ever | C．if not | D．if no |
The traditional approach ____ with complex problems is to break them down into smaller, more easily managed problems.
| A．to dealing | B．in dealing | C．dealing | D．to deal |
Someone called me up in the middle of the night, but he hung up ____ I could answer the phone.
| A．as | B．since | C．before | D．until |