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is good for one's health. is related to some illness. has been investigated long since. has no effect on the body.
open, has closed close, has been open open, has been opened closed, has been closed
was had been has been were
is; come is; have come has been; came has been; have come
was; entered is; entered into has been; entered B.＆C.
some time sometime sometimes some times
because than unless since
fact reality action practice
was provided has provided provided has been provided
It has There has We have There is
was ;meet was ;met has been; met is ;meet
has it been since ; for which is it before ; in which it is when ; that it is since ; for which
Is , begin has been , began has, been had been ,began
when; before since; before after; before before; since
has been；since had been；until was；after would be；before
are were have been has been
It has There has We have There is
has been ； since had been ； until was； after would be ； before
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