at 21:03. 3. @user70587 The third can (or should, depending on who you ask) be written with a comma; the fourth cannot be written with a comma under any circumstances. - LegionMammal978. Mar 2, 2018 at 23:58. @LegionMammal978 I'm a native speaker and I would use a comma in the fourth, but only if I want to convey a pause.
Toconstruct 'could have' and 'should have' we again use these same verbs, but now just add the infinitive form of haber and then the past participle of the main verb instead of the infinitive. Yo podría estar = I could be. Yo podría haber estado = I could have been. Yo debería estar = I should be.Accordingto Duke professor Harris Cooper, it's important that students have homework. His meta-analysis of homework studies showed a correlation between completing homework and academic success, at least in older grades. He recommends following a "10 minute rule": students should receive 10 minutes of homework per day in first grade, and 10
. #4. Should must be followed by a verb in present time, or at least that's the way I've always seen, so: Should be, should have, should learn, should say, ect. That's why the second one is wrong, it should be: 2 We should have invited. I hope it helps.