高中英语语法讲解2：现在完成时的用法
表继续：说明动作从过去一直持续到现在。
1、过去时：I began to work three years ago.
2、现在时：I still work now.
1+2=3 现在完成时：I have worked since three years ago.
现在完成时说的是过去发生的事，但必须和现在有关，否则就用过去时。
注意：
1、可从时间状语判断句子是否适用完成时：
She always play alone in the park for one hour every day.
这句话是一般现在时，因为它指的是一个客观情况，每天都独自公园玩一小时，时间状语every day也限定了时态为现在时。
2、通常，since引导的从句用过去时，主句是现在完成时，但“It"s+时间····”开始的句子例外。
It"s ten years since he gave his girlfriend a red rose.
表经验：动作发生在过去，但现在还有印象。
1、He was playing alone in the park.
2、 Now he remembers the park.
1+2=3 现在完成时：He has played alone in the park.
他曾独自在这个公园玩过。用现在完成时就表示过去的这个经历和现在有关，即暗指他现在还记的这个公园，或这个公园对他印象很深，所以3=1+2如果只用1就表示一个客观事实，与现在无关。
时间状语：
置于句中：often，ever，never，固定位，放在助动词have/has后，过去分词前。
We have often played in the park.
置于句末：表频率的副词 once，several times等
I have played alone in the park once.
置于句首：对时间提问的疑问词
How many times have you been to the park?
have/has been 用法：
have been to
I have been to America twice.(经验)
我曾去过美国两次。
I have been to the great wall.（完成）
我去长城了。
have been in
Have u ever been in London?(经验）
你曾在伦敦住过吗？
No, I have not been in there yet.
不，我还没在那住过。
We have been in museum for the whole day.（继续）
我们在博物馆呆了一整天。
说明：
have/has been to 用于“经验”，表示“曾去过···”时，常和often，once，twice等，频率副词连用。
I have often been to China.
注意：
have/has been in/to···句中后跟副词则不用to/in。
Have u been there?
We have been there for the whole afternoon.
表完成、结果：过去发生并结束的动作对现在产生的结果或影响。
“完成”的意思是“刚做完···”或“做完了···”表示过去开始的动作在说话前规格完成。
I"ve just filled in the registration form.(填表动作已完成，现在没在填表。)
比较：I filled in the registratiom form yesterday.(昨天填好表，和现在无关，现在有可能也在填表。)
They"ve gone to Sichuan.(去四川了，不在本地，在没在四川没表示。)
“结果”的意思是“做了···（现在是其结果）”。表示过去动作的结果对现在仍有影响，包含两个含义。
1、He invented TV.(过去的动作）
2、TV make our lives rich.（对现在的影响还在）
1+2=3、TV has made our lives rich.
1\John became a teacher.
2\John is a teacher.
1+2=3\john has became a teacher.
现在完成时和现在有关，对现在的影响很重要。
副词yet：
否定句；还。
疑问句：已经.
I haven"t filled in the registration form yet.
Has he filled in the registration form yet?
No, not yet.(not yet 常用来代替否定句)