_______ he met with the difficulty did he realize the importance of our help.
| A．Even though | B．Never until |
| C．Only before | D．Ever since |
It is widely believed that an apple which fell from its branches were the _______ for Newton’s discovery of gravity.
| A．intelligence | B．Acquaintance |
| C．application | D．inspiration |
Raising _______ retirement age in progressive steps is in _____ line with China’s labor market realities and should be prioritized, an official said Tuesday.
| A．the ; / | B．/; the |
| C．/; / | D．the; the |
It was not until 1911, _______ the first vitamin was identified, _______ people realized the importance of it．
| A．when; which | B．when; that |
| C．that; which | D．that; that |
We should think carefully about ______ Mr. Needham said at the meeting.
| A．that | B．what | C．which | D．/ |
Have you ever met with this case in your life you can't understand others even if they have said something several times？
| A．where | B．what | C．that | D．which |