There are some health problems that, when ______ in time, can become bigger ones later on.
| A．not treated | B．not being treated | C．not to be treated | D．not having been treated |
28．He spent much of the evening with Robert Green,____he had hardly seen in the thirty years since they had worked together at CBS.
| A．what | B．that | C．who | D．Whom |
27．At last, the boys found themselves in a pleasant park with trees providing shade and____down to eat their picnic lunch.
| A．to sit | B．sat | C．sitting | D．having sat |
26．The researehers delermine what type of plants the virus can infect(感染) and____insects can carry the virus.
| A．those | B．why | C．which | D．How |
25．—Did you get my letter?
—I received one just as I____.
| A．set out | B．had set out | C．was setting out | D．would set out |
24．When she called at his studio, she____that he had gone to Japan.
| A．is told | B．was told | C．tells | D．Told |