单选题 Although they plant trees in this area every year, the tops of some hills are still ______.

单选题 I have heard both teachers and students ______ well of him.

单选题 I'm very sorry to have ______ you with so many questions on such an occasion.

单选题 He came back late, ______ which time all the guests had already left.

单选题 His remarks left me ______ about his real purpose.

单选题 If the whole operation ______ beforehand a great deal of time and money would have been lost.

单选题 The price of beer ______ from 50 cents to $4 per liter during the summer season.

单选题 The house was very quiet, ______ as it was on the side of a mountain.

单选题 Our son doesn't know what to ______ at the university; he can't make up his mind about his future.