1. Both are fine. B is more common. 2. Both are fine. Often you'll add "a day" to it. E.g. "The doctor told me to take these three times a day, every two days, for a fortnight". 3. There's nothing really wrong with this, I don't think (except a missing 's' on the second "group"). Other ways to say it might be: - We have three groups of eight people. - There are eight people in each group and three groups in total. 4. Both are ok. You could include "that we still need to" in B if you wanted: - There are many problems that we still need to discuss at the next meeting. 5. B and C are incorrect, I think. A is close, perhaps: - I am going to start now, in order to not miss the beginning. (Note the position of "to") Other options are: - I'm going to start now, so that I don't miss the beginning. - I don't want to miss the beginning, so I'm going to start now. As an aside, "correct by grammar" is a bit if an awkward phrase. We would usually say "grammatically correct". - Could you check my sentences and let me know if they are grammatically correct.