If nothing________，the oceans will turn into fish deserts(2013·湖南，26)

What lessons do you have on Wednesday afternoon—We have ________ Art lesson and ________ PE lesson.

Don’t you know your computer has been infected with viruses?— Really, no wonder it hasn’t ________ as well as before. [ ]

It is not always easy for the public to see _______ benefit a new invention can be of to human life.

How long _______ in Shanghai?—I will be there attending a conference and giving a speech, which will take about 3 days