It is reported that North Korea has conducted another underground nuclear test.

He is an expert in experimental psychology.

He is spending a lot of time on experimental research.

Happy New Year, Ka.

I will hold my birthday party on the fourth day of the month.

He draws a four-panel comic strip every day.

I draw a four-frame comic strip every day.

He is a mayonnaise freak, always slathering plenty of mayonnaise on his sandwiches.

This old radio uses a tetrode.

My father is forty-one years old.