I'm still not completely clear on this. I recently found this in the OG 12
. Does anyone else have any comments on this?OG 12
says that--in the following example --the verb following after (or once) should be in the present-perfect tense to indicate that the trimming must occur before the tourists arrive.
"A proposal has been made to trim the horns from rhinoceroses to discourage poachers; the question is whether tourists will continue to vist game parks to see rhinoceroses once
the animals' horns have been
Can anyone please explain if this is a general rule, or if it was just specific to this question.