The photograph shows a sample of stained frog blood cells as viewed with the high-power objective of a compound light microscope, with a specific structure labeled "A". Which of the following is the BEST description for the structure labeled "A?"
A Chloroplast that carries out photosynthesis
B Lysosome that stores hydrolytic enzymes
DC Mitochondrion that produces ATP
OD Nucleus that regulates cell activity

Note: You will find the photograph in the attached files.

The Nucleus that regulates cell activity

Explanation:

The structures labeled with the "A" are the nucleus of erythrocytes.

Frog´s erythrocytes might be about 50μm, are ovoid and biconvex, and present a nucleus with condensed chromatin. They are stained red by eosin and the nucleus by hematoxylin. DNI is the stained material in the cell.    

c) 50% there are four chromosomes. after crossing over, 2 of the four have been changed. that means any gamete has a 2 in 4 chance or 50% chance of receiving the mutated chromosome.