_____on the grass _____singing and laughing.
| A．Seated ; is some students | B．Seated ; are some students |
| C．Sitting ; is some students | D．Sitting ; some students are |
. _________ many times, he finally understood it.
| A．Told | B．Telling | C．Having told | D．Having been told |
The chairman thought _________ necessary to invite Professor Smith to speak at the meeting.
| A．that | B．it | C．this | D．him |
. It was not until nearly a month later _________I received the managers reply.
| A．since | B．when | C．as | D．that |
---- What do you think of the book? ---- Oh, excellent .It is worth __________ a second time.
| A．to read | B．to be read | C．reading | D．being read |
. Such animals like dinosaurs died out because they could not _________ to the change of the climate.
| A．suit | B．keep | C．adapt | D．switch |