When doing medical research with human subjects, which four limitations are unavoidable? It’s often impossible to repeat trials on the same subjects.
Subjects may report an inaccurate medical history.
It can be difficult to control all possible variables.
It’s impossible to come up with testable scientific questions for human subjects.
There are ethical or privacy concerns to consider.

In 1959, doctors began using the powerful antibiotic methicillin to treat infections of staphylococcus aureus, but within two years, methicillin-resistant strains of s. aureus (mrsa) appeared. how did the resistant strains of s. aureus emerge? in 1959, doctors began using the powerful antibiotic methicillin to treat infections of staphylococcus aureus, but within two years, methicillin-resistant strains of s. aureus (mrsa) appeared. how did the resistant strains of s. aureus emerge? staphylococcus aureus bacteria that were able to synthesize cell walls using a protein that was not affected by methicillin survived the methicillin treatments and reproduced at higher rates than did other individuals. over time, these resistant individuals became increasingly common. in response to treatment of staphylococcus aureus infections with methicillin, some bacteria began to synthesize cell walls using a protein that was not affected by methicillin. these bacteria survived the methicillin treatments and reproduced at higher rates than did other individuals. over time, these resistant individuals became increasingly common. in response to treatment of staphylococcus aureus infections with methicillin, bacterial populations gradually began to synthesize cell walls using a protein that was not affected by methicillin.

Multicellular organisms use cell division, mitosis, for growth and the maintenance and repair of cells and tissues. single-celled organisms may use cell division as their method of reproduction. regardless of the reason for mitosis, the process ensures genetic continuity. what is the step in the cell cycle that ensure genetic continuity?

Ascientific idea becomes valid when it is what?