Speeding and blocking are traffic offences which lead to . . . . . . accidents.

The correct answer is C. gruesome.

Speeding and blocking are traffic offences which lead to serious accidents. These accidents can cause serious injuries or even death.

Option A, winsome, is not the correct answer because it means attractive or charming.

Option B, urban, is not the correct answer because it means relating to or characteristic of a city.

Option D, minor, is not the correct answer because it means not important or serious.