21.现在进行时
现在进行时由“am，are，is+现在分词”构成，主要表示：
1.现在正在进行的动作：
i'm waiting for the bus．
我正等公共汽车。
she's sitting in an armchair．
她正坐在沙发椅上。
what are these people doing?
这些人在干什么?
it is snowing．
在下雪。
2.预计将要发生的动作(仅限于少数趋向性动词)：
tomorrow they re going to new york．
明天他们将动身去纽约。
my cousin is arriving next week．
我表弟下星期到。
3.be going to结构表示“打算做某事”或“即将发生某事”:
miss green is going to wear a blue dress．
格林小姐打算穿一件蓝色连衣裙。
i'm afraid it's going to rain．
恐怕要卜雨了。
4.句式：
1).肯定句:
i'm having lunch.
you (we, they)'re having lunch.
he (she)'s having lunch.
2).否定句:
i'm not having lunch.
you (we, they) are not having lunch.
he (she) is not having lunch?
3).疑问句:
am i having luch?
are you (we, they) having lunch?
is he (she) having lunch?
4).简短回答:
yes, i am．
yes, you (we, they) are.
yes, he (she) is.
no, i'm not.
no, you (we, they) aren't.
no, he (she) isn't.
情况 加法 例词
一般情况 加一ing go-going; study-studying
以不读音的e 结尾 去e ，再加一ing live-living; move-moving
以重读闭音节结尾，末尾又只有一个辅音字母 把末尾辅音字双写，再加一ing sit-sitting; win-winning; begin-beginning（但open-opening)