But a lot of problems are coming about. Traffic in cities is getting heavier and heavier. The car is causing more pollution. To solve these problems, something must be done.

　　此篇書面表達(dá)的中心“轎車進(jìn)入家庭后所產(chǎn)生的影響”，由兩個(gè)主題句 It has advantages 和 A lot of problems are coming about 體現(xiàn)出來。為了進(jìn)一步展開主題句 It has advantages，文章從convenience, saving time and developing car industry and economy 三方面加以論證;為了展開主題句 A lot of problems are coming about，文章從 traffic 和 pollution 兩方面加以說明。這樣利用主題句使文章層層相扣，形不散，神也不散，文章讀起來朗朗上口，生動有趣。