We use the past perfect continuous tense to show that an action started in the past and continued up until another time in the past.
我们用过去完成进行时态来形容一个在过去开始的行动，这个行动持续到过去的另一个时间。
Today, we are going to talk about the present perfect continuous tense.
今天，我们谈谈什么是现在完成进行时。
The question is in the present perfect continuous so you will answer with the verb in the continuous.
For example：这个问题是用现在完成进行时来提问的，所以回答时也用进行时态的这个动词。
We use the future perfect continuous tense to talk about how long an action will be going on at a future time.
我们用将来完成进行时态来形容一个行动在未来特定的时间里已进行多久了。
The second function of the present perfect continuous tense is to talk about an action that started in the past and it is still happening.
第二种：谈论一个起始于过去，但是现在仍在发生的动作。
The theoretical error in five axis NC machining, which is resulted from approximating the perfect continuous tool path with discrete linear segments, is strictly analyzed.
对五坐标曲面加工中由离散线性运动逼近理想刀具轨迹所引起的理论加工误差进行了较严格的分析。
We use the present perfect continuous (I have been doing) for situations over a short time. We use the present perfect (I have done) for situations that exist for a longer time.
现在完成进行时用在短时间的情况，现在完成时用于长时间的情况。
We use the present perfect continuous (I have been doing) for situations over a short time. We use the present perfect (I have done) for situations that exist for a longer time.
现在完成进行时用在短时间的情况，现在完成时用于长时间的情况。
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