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Which is the best way to write this sentence?
This system was designed to study the effects of climate change and anthropogenic pollution on microbial communities under highly controlled conditions and has already been validated
or
This system was designed to study the effects of climate change and anthropogenic pollution on microbial communities under highly controlled conditions was already validated
Thanks!
has been implies the validation is still in effect.
If you use was, you might write:
The system was certified as producing valid results in 2007, and the certificate expired in 2011.
Saying the system was validated doesn't prohibit something to happen later that invalidated it again.
