Name one disadvantage of light microscopes

Limitations
Light microscopes can magnify specimens or objects up to fifteen hundred times their actual size. This is amazing if you consider objects naturally visible to the eyes. But when you consider microscopic specimens then the magnification is not very impressive. Also the depth of field is confined. For very specific observations of elements or specimens that are smaller than 0.275 microns or smaller than half the wavelength of white light require electron microscope.

the correct answer is: b. pantala flavescens, because these organisms would have a high level of genetic variation due to sexual reproduction.  

because involves two organisms (parents) whose genetic material combines, sexual reproduction leads to genetic variation in new generations of offspring. the offspring is an unique organism, with new genome, more protected with the higher ability to adapted. this process is fundamental to evolution.