How can the heart be strong enough to pump blood up your legs against gravity? How can we differentiate so many different foods if we can only taste four flavors on our tongue: sweet, bitter, sour, and salty?
How can we unlock the 90% of our brain that we never use?

The heart is not strong enough by itself to get the blood back up the veins in your legs and back to your heart.  So it is a combination of blood pressure from the heart's pumping action, the valves, and muscle movement that gets the blood up the legs against gravity.It is often concluded, therefore, that the heart works only against the viscous resistance of the system, not against gravity, even in vascular loops above the heart in which the siphon principle operates.

How do we detect the taste of different types of food we eat?

Taste buds have very sensitive microscopic hairs called microvilli (mykroVILLeye). Those tiny hairs send messages to the brain about how something tastes, so you know if it's sweet, sour, bitter, or salty.

The greatest danger to your brain is not the possibility that a large portion is going on unused. Rather, the greatest dangers are stroke, Alzheimer's disease, and tumors. The best ways to protect yourself from such risks include eating healthy, exercising, and getting enough rest

Explanation:

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Explanation:

The heart is not strong enough by itself to get the blood back up the veins in your legs and back to your heart. ... So it is a combination of blood pressure from the heart's pumping action, the valves, and muscle movement that gets the blood up the legs against gravity

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.