The professor requested that all the students _______ the reports at once.
| A．would hand in | B．hand in | C．handed in | D．handing in |
Joan had often heard ____ said that Marley had no money.
| A．one | B．it | C．once | D．her |
Carl Linnaeus made great contributions to ________ plant species.
| A．group | B．have grouped | C．grouping | D．been grouping |
He observed a stranger _______ around the store at 12 p.m. last night.
| A．to hang | B．hang | C．hanging | D．to be hanging |
Once ______ , the plan can’t be changed.
| A．begin | B．beginning | C．began | D．begun |
They asked me so many ______ questions that I got ______.
| A．confusing; confusing | B．confused; confusing |
| C．confused; confused | D．confusing; confused |