Carbon
dioxide from burning fuels is the most common of the so-called greenhouse gases.
| A．produced | B．producing | C．to be produced | D．having been produced |
Thirty dollars ________ too expensive.
| A．are | B．is | C．were | D．be |
The number of pages in this dictionary ________ about two thousand.
| A．are | B．has | C．have | D．is |
Now Tom with his classmates ________ football on the playground.
| A．play | B．are playing | C．plays | D．is playing |
Half of the workers here ________ under 30 ________.
| A．is;years | B．are;year old | C．is;years old | D．are;years of age |
About 60 percent of the students ________ from the south,the rest of them ________ from the north and foreign countries.
| A．are;is | B．are;are | C．is;are | D．is;is |