He accidentally rode his bicycle onto the curb.

The tough base of this mushroom is very hard.

Studying the history of the Middle Ages is very interesting.

We need mutual understanding.

He believes in 'an apple a day keeps the doctor away', so he eats fruit every day.

Research on xenotransplantation has the potential to open new frontiers in medicine.

This river has a lot of small stones.

This rock is a type called nepheline.

He stumbled many times in the new project, but eventually succeeded.

May good luck come to you.