When eukaryotes make mRNA, they add a 5' cap and a poly-A tail to protect the mRNA from being destroyed by ribonucleases (enzymes that break down RNA). But why do cell have ribonucleases to begin with? Why would cells to break down the mRNA it went through all the trouble to make? Use an example to explain your answer.

the answer is c.) there is a warm front in region a and a stationary front in region b.

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added