The scientists of the research center keep the good habit of summing up their experience ______ time to time.
举一反三
- _______ more time, the scientists will be able to work out a good solution to the problem.
- We must make up for(弥补) lost time. Lost time __________.
- Get in the habit of looking back when you travel, especially at the time of getting up to leave somewhere. ( )
- I have_______ good friends, so I feel__________ from time to time.
- We no longer keep up the close friendship of few years ago, though we still visit each other on occasion. A: in good time B: up to date C: now and then D: once and for all