Answer:
Minivalves
Explanation:
Lymphatic capillaries are so much permeable that some researchers thought that they are open from one side but scientists found that this permeability is due to some structural modification.
The endothelial cell that forms the lymphatic capillaries wall are not packed tightly and overlap each other very loosely which makes easy openings in the structure called mini valves.
When the pressure of fluid in interstitial space is high then the mini valves become open and allow the fluid to enter the lymphatic capillary. So mini valves are the unique structural modification that increases permeability in lymphatic capillaries.
I think the answer is vibrssae or whiskers.
Answer: A: Its fertile oases enabled farmers to grow enough food for themselves and for sale.
Explanation: The Arabia region is a region located within the Arabian desert. A desert is an area of extreme heat, often dry weather condition with barren lands that cannot support agriculture and food production. An oases on the other hand is a region of luscious, cultivate-able land within a desert.
Food is one of the most important basic needs of man and hardly can anyone survive without food for more than twenty days. Hence, the presence of oases within the otherwise dry environment of the Arabia region is a major protection against death from hunger.
Taking a closer look at other options, none of them guarantees food supply and income to the Arabia region unlike food production in oases. Hence, the fertile oases is really the most important factor that serves as protection in the region's history.
Correct option: A
