It looks like you need help completing the comparisons in your sentences. Here are the suggested completions for the sentences you've provided:

8. Mary is shorter than her sister.
⇒ Mary's sister is taller than Mary.

10. City life is not as boring as country life.
⇒ Country life is more boring than city life.

11. Traveling to work by bus is not as convenient as traveling by private car.
⇒ Traveling to work by private car is more convenient than traveling by bus.

12. My village is noisier than her village.
⇒ Her village is quieter than my village.

Feel free to let me know if you need any more assistance!