英语语法they have been friends ever since they were in grade sch

1.they have been friends ever since they were in grade school.这句话中have been friends 是什么用法?
Answer:
英语时态-现在完成时其意义在于表示"过去某一时间开始并一直持续到现在的动作或状态"或 "过去发生并且已经完成的动作对现在造成影响或后果"
此句中用be动词的现在完成形式表示"过去是现在仍然是"
2.they were in the grade .是什么用法?是主系表吗?were,in the grade 是什么成分?
Answer:
(1)断句有误,grade school 小学 不应该把它们分开
(2)是主系表结构
(3)They (主语)were (系动词) in the grade school (介词短语作表语)
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ever since 是从....时候开始的意思，引导一个时间状语从句，是现在完成时的标志，因此主句they have been friends要用have been（完成时态），后面是系表结构，介词短语in grade school作表语，整句话的意思是：他们从小学开始就是朋友了。

1.they have been friends ever since they were in grade school.这句话中have been friends 是什么用法？
Answer:
have been friends 是be动词的现在完成时态的用法，因为后面的时间状语是由since引导的，表示从过去的某一时刻开始一直到现在的状态，句子要用现在完成时。
2.t...

they是整个句子的主语，have been是整个句子的谓语，ever到最后做时间状语，grade school是小学的意思。

主句they have been friends 构成现在完成时，表示已经发生的状态或者是持续的状态，该句意思是，小学开始他们就是朋友了，后面的they were in grade school是时间状语从句中的从句，从句的主语是they，系动词were，表语是in the grade school（grade school是小学的意思），构成主系表结构。
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现在完成时的用法。since they ere...是做时间状语从句。在这个从句中是主系表结构，were是系动词，in the grade school是表语。

Have been是现在完成时，表示从过去某一刻至今一直是。
they were in the grade 是主，系，表结构。
were是系动词，in the grade是介词短语作表语。