This pig iron is a raw material for making high-quality steel.

We need to devise a new strategy.

I went to Tokyo the week before last.

He is traveling around the world in search of the elixir of life.

He is undergoing training for extravehicular activity.

He engaged in an extravehicular activity from the spaceship.

He is studying about ancient military tactics.

This is a linear mathematical problem.

This equation is linear.

They waged war against the enemy country.