Compared with the nature forces, our power was so weak that all our efforts to save our homes from the earthquake were __________.
He always helps us ________ he is doing when we turn to him for help.
—How many photos have you taken? —I’ve taken 60 ________. I’ll take more.
With the popularity of network, email has largely ________ the traditional letter.
Many students, ________ some pocket money and social experience, work during their holidays.
He likes books ________ science because he wonders what and why our world is.