However, at times this balance in nature is ______, resulting in a number of unforeseen effects.
| A．troubled | B．disturbed | C．confused | D．Puzzled |
John was given the same suitcase his father and grandfather _______with them to school.
| A．took | B．had taken | C．were taking | D．would take |
When I talked with my grandma on the phone ,she sounded weak , but by the time we ____up ,her voice had been full of life.
| A．were hanging | B．had hung | C．hung | D．would hang |
—Why does the lake smell terrible ?
--because large quantities of water ____.
| A．have polluted | B．is being polluted | C．has been polluted | D．have been polluted |
My parents have promised to come to see me before I ___for Africa.
| A．have left | B．leave | C．left | D．will leave |
The way the guests____in the hotel influenced their evaluation of the service.
| A．treated | B．were treated | C．would treat | D．would be treated |