26．Even if there is no scientific proof yet ______ secondhand smoke causes cancer, there is no reason why nonsmokers should be forced to take this risk．
| A．which | B．that | C．when | D．Where |
Diamond, _________, is the hardest of all materials.
| A．like we know | B．since we know | C．we know | D．as we know |
He is not such a man ________ cares for himself only.
| A．who | B．that | C．whom | D．as |
—Tomorrow is a holiday. Why are you doing your homework now?
—I am doing these exercises so that I won’t have tomorrow.
l
| A．to | B．it | C．them | D．for |
I like getting up early in summer. The morning air is good.
| A．to be breathed | B．being breathed | C．to breathe | D．breathing |
Tell me you want your coffee, black or white?
| A．how | B．when | C．which | D．what |