"Four people so far have followed that line of research," he said.

I wanted to continue along a certain line of research.

We will certainly follow up on that line of research.

I am very much preoccupied at present with various lines of research and study.

"That line of research seemed to lead me up against a blank wall."

The whole line of research was being closed up as a mistake.

The line of research is too new to have allowed studies that track people over several years.

We just wrote it off to a hot line of research.

There have been similar lines of research to this method.

I think you have set yourself a new, very interesting, and difficult line of research.