Though she doesn't speak English well, but she works in a foreign company.

• Error: B (Remove "but") Correction: Though she doesn't speak English well, she works in a foreign company.

Remember not to skip the breakfast because it's the most important meal.

• Error: No error.

If you did more exercise, your muscles will be stronger.

• Error: A (Change "did" to "do") Correction: If you do more exercise, your muscles will be stronger.

I don't like people who talk loud in public places.

• Error: C (Change "loud" to "loudly") Correction: I don't like people who talk loudly in public places.

Nobody liked to eat this kind of food here, didn't they?

• Error: D (Change "didn't" to "did they") Correction: Nobody liked to eat this kind of food here, did they?