--- No wonder I often hear her sing in the garden.

　　A. had taught

　　B. taught

　　C. is teaching

　　D. has taught

　　20. Occasions are quite rare ________ I have the time to spend a day with my kids.

　　A. why

　　B. who

　　C. which

　　D. when

　　（二）阅读理解：

　　A

　　NASA scientists said on June 1, 2008 they had found ice on Mars -- a step towards finding evidence of life.

　　Sharp new images received from their Phoenix lander convinced scientists that the spacecraft's thrusters had uncovered a large patch of ice just below the Martian surface, team members said.

　　That bodes well for the mission's main goal of digging for ice that can be tested for evidence of organic compounds that are the chemical building blocks of life.

　　Washington University scientist Ray Arvidson said the spacecraft's thrusters may have blown away dirt covering the ice when the robot landed one week ago.

　　Scientists said a detailed image taken under the lander shows one of the craft's three legs sitting on coarse dirt and a large patch of what appears to be ice -- possibly 3 feet (0.9 metres) in diameter -- that apparently had been covered by a thin layer of dirt.

　　"We were worried that it may be 30-, 40-, 50-centimeters deep, which would be a lot of work. Now we are fairly certain that we can easily get down to the ice table," said Peter Smith, a University of Arizona scientist who is the chief project investigator.

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