She is not certain about __________ she has done anything wrong.
| A．if | B．whether | C．that | D．What |
In order to meet the deadline, Professor Smith along with his assistantsthe project day and night.
| A．work on | B．works at | C．is working on | D．are working on |
Although dragon doesn’t exist, we still take it as a _______ of our nation.
| A．example | B．sign | C．mark | D．symbol |
Baseball requires teamwork _______ tennis is an individual sport.
| A．while | B．when | C．yet | D．although |
--- The earthquake last night was really terrible.
--- ______, no people were injured or killed, and they escaped in time.
| A．Hopefully | B．Luckily | C．Sadly | D．Unfortunately |
Scientists say it may be five or six years _____ it is possible to test this medicine to human patients.
| A．since | B．after | C．before | D．when |