His parents asked him to buy books ______ he found useful and necessary for his study. A: whichever B: whatever C: whenever D: however

It is true that there are still abundant reserves of metals which have not yet been______, but it is necessary to take steps to ensure that alternative materials are substituted whenever possible. A: utilized B: mobilized C: acquired D: cultivated

that all the risks should be calculated in advance. A: This is necessary B: Which is necessary C: That is necessary D: It is necessary

We consider _____ lessons should be previewed before the class. A: that it necessary B: it that necessary C: it necessary that D: necessary it that

I find ____________ to make some changes. A: it is quite necessary B: that is quite necessary C: it quite necessary D: quite necessary

If_____, we’ll continue our experiment after office hours. A: being necessary B: be necessary C: is necessary D: necessary

Fill in the blanks with the proper words or expressions given below, changing the form if necessary.Whenever I see him, I cannot but______ at his strange hair style.

Choose the correct meaning based on the expression's meaning in the context.5. crossed my mind A: whenever I forget B: whenever I think of it C: whenever I study hard D: whenever I put my arms over my head in the shape of a cross

If_____,<br/>we’ll continue our experiment after office hours. A: being necessary B: be necessary C: is necessary D: necessary

We consider ____university students should do more reading during their spare time. A: necessary that B: necessary C: it necessary D: it necessary that