Just a few years ago, biologist and medical personnel were surprised to learn that fetal cells can escape and enter the mother's blood. how can these cells be used in fetal testing?

Ascientist is designing an investigation to study the impact of invasive bird populations on local, native bird populations at backyard bird feeders. what population is most likely to be a control group for the investigation? amount of food number of bird feeders invasive bird populations local backyard birdfeeders without food