This math problem includes multiple variables.

This town has greatly changed over the past 50 years.

A report arrived at the police that he died from an unnatural cause.

I am waiting for his letter of reply.

I didn't have time to write back to him.

It seems this wine has spoiled.

This wine will change (deteriorate) over time after it's opened.

Geomorphology is the science that studies the surface shape of the earth.

He is writing a thesis on geomorphology.

I opened the atlas and planned the travel route.