Solving a quadratic equation is difficult.

Reijiro is my best friend.

Redistribution of this software is prohibited.

As the phrase 'If it does not sing, let's wait until the cuckoo sings' suggests, we should wait patiently until the opportunity comes.

He has done everything he can to prepare for the exam, and now he is in a state of 'doing all that is humanly possible and waiting for fate to take its course'.

She was going through puberty and was confused by the changes in her body.

In behavioral sciences, the use of metatools plays a crucial role.

World War I was a large-scale war that lasted from 1914 to 1918.

World War II lasted from 1939 to 1945.

Let's pray that World War III does not occur.