Which sentence states a central idea in "Cool Jobs Part 1"?

Cool Jobs Part 1


1. They swabbed every place the burglars had touched, looking for bacteria and other microbes the women might have left behind.

2. If you touch a surface, you leave behind millions of bacteria and other microbes.

3. One issue is that the science of analyzing microbial DNA is still imprecise.

4. Each sample tends to hold hundreds of thousands—or even millions—of single-celled organisms.