控制绝症（controlling cancer）
there are two main caue of cancer: heredity and environment. we can do nothing to change our heredity, that i, the baic phyical characteritic that were paed on to u by our parent. however, we can do a great deal to control our environment, which may account for 80-90 %of all cancer.
environmental pollution can be divided into two kind: peronal and imperonal. peronal pollution may be defined roughly a unhealthy habit uch a moking, drinking, and eating the wrong food. clearly, with enough will power we can control thi peronal environment.
imperonal pollution, on the other hand, refer to thoe thing which are beyond our individual control. one example would be indutrial pollution, which i very hard to control becaue of the expene involved. it would be expenive in term of profit and perhap job. the american automobile indutry, for example, reited the law requiring mog-control device becaue it feared the added expene would reduce profit. neverthele, ome law protecting the environment have been quite ucceful in reducing pollution.