I haven't heard any news from him at all.

In this experiment, we will use the International System of Units.

An identity matrix is a square matrix in which all the elements on the diagonal are 1 and all other elements are 0.

An imaginary unit is an important concept in mathematics.

An astronomical unit represents the average distance from the Earth to the Sun.

This product has a very small assembly unit.

This month's expenses are too high, I have to save money.

He sneaked into the house in the middle of the night.

This book is no longer available anywhere.

He became good at playing the piano, and finally acquired the skill.