1） It is usually the case that

　　2） It is plain common sensethe more/lessthe more/less

　　3） The serious reality had taught us a lesson： not being environment friendly will be avenged mercilessly.

　　4） As a proverb says/as is known to all/as a popular saying goes，

　　5） I can think of no better illustration than an English poem/adage which goes like this：

　　6） The old story ofcan serve as a good illustration that