This software has backward compatibility.

It's difficult to understand the context of this sentence.

This eigenfunction is one of the fundamental concepts of quantum mechanics.

The poster girl of that shop is very kind and always welcomes customers with a smile.

This old radio uses a cold-cathode tube.

The launch of intercontinental ballistic missiles has become an international issue.

It is said that secondhand smoke has a negative impact on health.

Topology is a branch of mathematics that abstracts and generalizes the concept of space.

He was infected with hepatitis E.

He is receiving treatment for hepatitis C.