The soda－acid portable extinguishers must be discharged and refilled _____.A.every six mon

These acid residues must be prevented from entering the crankcase, otherwise the lube oil would be .

According to the passage, which of the following is true of acid rain？A．Tree leaves die of

The type of extinguisher which should be used for an electric fire is ______.A.carbon diox

The latest discs, used for small portable computers,______3,600 times a minute.A．rotateB．r

Compared with 1980s, what is the biggest development of portable computers in 1990s？A．They

What will soda makers do in response to the ban？A．They consider taking legal actions again