It is bad manners to ________an invitation without a reason.
| A．break down | B．settle down | C．turn down | D．calm down |
_______ basic first-aid techniques will help you respond quickly to emergencies.
| A．Known | B．Having known | C．Knowing | D．Being known |
People develop _______ preference for a particular style of learning at _______ early age and these preferences affect learning.
| A．a; an | B．a; 不填 | C．不填; the | D．the; an |
—Is the chemistry experiment easy? —______. I’ll just do my best.
| A．I think so | B．Certainly | C．Not a little | D．Anything but |
The number 5.12 is a special number,__ ,I think, that will be remembered by Chinese people forever.
| A．what | B．it | C．which | D．one |
The country has already sent up three unmanned spacecraft, the most recent__at the end of last March.
| A．has been launched | B．having been launched |
| C．being launched | D．to be launched |