1.一般现在时表示经常性或习惯性的动作及现在所处的状态

常和always(总是)，regularly(有规律地)，usually(通常)，often(经常)，sometimes(有时)，every day(每天)，every week(每周)，seldom(难得)等时间状语连用。

Normal tourism is often bad for the environment，and tourists often cause problems．(人教大纲版高一上第20页)

普通旅游往往不利于环保，游客常常会招来问题。

They are careful about what they eat and exercise regularly．(人教大纲版高二上第44页)

人们注重饮食，并定期运动。

Sometimes I go to bed at about11 p.m．

有时我大约在晚上11点上床睡觉。

The situation changes from day to day．

形势每天都在发生变化。