But there is not single convenient explanation which covers all the cases.

But I couldn't come up with one single explanation.

There is never a single, simple explanation for the evil they do.

Is there any single explanation that could cover the whole list?

I've puzzled over this for weeks without coming up with a single explanation.

There is no single explanation for why Paris works so well.

I went home to my family then, and they took me back without asking for a single explanation.

For many groups there is no clear single explanation.

But what exactly makes these people part of a "general phenomenon" for which there can be a single explanation?

There were complicated machines that he could run without trouble after a single explanation.