[单选题] Having been ill in bed for nearly a month, he had a hard time ________ the exam.

1、[单选题]________ such heavy pollution already, it may now be too late to clean up the river.

• A、Having suffered
• B、Suffering
• C、To suffer
• D、Suffered

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2、[单选题]You were silly not ________ your car.

• A、to lock
• B、to have locked
• C、locking
• D、having locked

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3、[单选题]The research is so designed that once ________ nothing can be done to change it.

• A、begins
• B、having begun
• C、beginning
• D、begun

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4、[单选题]Robert is said ________ abroad, but I don’t know what country he studied in.

• A、to have studied
• B、to study
• C、to be studying
• D、to have been studying

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5、[单选题]Don’t leave the water ________ while you brush your teeth.

• A、run
• B、running
• C、being run
• D、to run

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