_________ that causes heavy haze sweeping over china remains unknown to many scientists.
| A．what it is | B．what is it |
| C．who is it | D．who it is |
相关试题
—I’m afraid I can’t afford a ticket to the concert, so I won’t be able to go with you.
—Don’t worry. It’s my ________.
| A．pleasure | B．treat | C．business | D．invitation |
—Hi, Li Xiaoxia. What a surprise! Dad _____ you _______ so early. He’s upstairs reading. I’ll just call him.
| A．didn’t know; would come | B．doesn’t know; are coming |
| C．hadn’t known; were coming | D．hasn’t known; will come |
—Where is Lu Wenjie? 
—I have no idea．He__________ be in the library.
| A．can | B．must | C．might | D．shall |
______difficulties we may come across, we' ll help one another to overcome them.
| A．However | B．Wherever | C．Whenever | D．Whatever |
相关知识点
推荐套卷
粤公网安备 44130202000953号