1.1.So much dust had accumulated during our absence that it look us some time to make the place spick and span.
1.2.So much dust had gathered during our absence that it look us some time to put the place in good order.
2.1. Iím dubious about entrusting the job to him, because he is neither shrewd nor discreet.
2.2. Iíve some doubt about trusting him with the job, because he is is neither wise nor careful.
'wise nor careful' does not mean 'shrewd nor discreet'[/B].
5.1. I chose at random, but my choice proved (to be) correct.
5.2. I chose without thinking, but my choice proved (to be) correct.
6.1. He does not seem to have any ambition in the world, but is just content to drift along.
6.2. He does not seem to have a purpose or aim in life, but is just content to drift along.
The others are acceptable.
Student or Learner