Celery stalks that are immersed in freshwater for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this, we can deduce that the freshwater .

hypertonic to fresh water but hypotonic to the salt solution

Explanation:

When the celery stalks are immersed in the freshwater the cells are  hypertonic to the fresh water this indicate the freshwater is the hypotonic solution. Thus the water moves inside the hypertonic cells and the cells of the celeray stalks becomes hard and stiff due to the development of the turgor pressure inside the cells of the stalks.  

The later, the salt water act as hypotonic for the cells.

c

explanation:

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.