In the vertebrate eye, what structure controls the amount of light that reaches the retina?
A. fovea
B. cornea
C. iris
D. lens
E. sclera
C. iris
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The period of time between exposure to an agent and the onset of disease signs and symptoms is called the
A. prodromal phase. B. decline phase. C. incubation period. D. lag phase.
The water vascular system of the sea star ________
a. is based on ampullae inside each of the tube feet, which contract to lengthen the foot for locomotion b. is a simple digestive system that expels coarse, undigested residues through the mouth c. is an open circulatory system d. flushes millions of eggs from the gonad
In all ecosystems, the biomass of primary producers is greater than the biomass of herbivores
Indicate whether the statement is true or false
A scientist wants to study the effect of vitamin C on colds. He recruits 100 people with colds and gives the experimental group 1000 mg of vitamin C per day. What would be an appropriate control?
A. Give the control group orange juice every day. B. Give the control group nothing. C. Give the control group 1000 mg of another brand of vitamin C per day. D. Give the control group 2000 mg of vitamin C per day. E. Give the control group a pill similar to vitamin C but containing sugar (a placebo).