—How do you think he managed to improve his English in such a short time?
—______ four hours on it every day．
| A．Because of spending | B．To spend |
| C．By spending | D．Spending |
Common sense requires us to get away from the concept that national boundaries are frontiers _________ knowledge may not spread.
| A．with which | B．across with |
| C．through which | D．from which |
—Could you say something about Turkey’s downing of the Russian fighter jet?
—Sorry. It ______ by a group of experts and will be made clear the moment they get the answer.
| A．has been investigated | B．is being investigated |
| C．was investigated | D．was being investigated |
Just as Tu Youyou once commented, “In order to make some achievements and ______ yourself in your field, there are certain things you must do.”
| A．bury | B．promote |
| C．distinguish | D．behave |
With the word PM 2.5 ________ appearing in media reports, people pay greater attention to it and seek health tips for smoggy days.
| A．immediately | B．consequently |
| C．permanently | D．constantly |
Finally, developing teenagers’ critical thinking should be a(n) ______ for education committed to helping students become competent citizens.
| A．motivation | B．inspiration |
| C．priority | D．responsibility |