Grammer sentence questions

1. Many companies make sugar-free soft drinks, which are flavored by synthetic chemicals; the drinks usually contain only one or two calories per serving.

2. Mr. Leyland played the viola professionally for many years, and he now conducts a community orchestra.

3. The crab grass was flourishing, but the rest of the lawn, unfortunately, was dying.

4. The hill was covered with wildflowers; it was a beautiful sight.