Which of the following decreases the reliability of results from a clinical trial?
a. an obsolete medical treatment
b. a double-blind technique
c. a short observation period
d. a voluntary enrollment plan

The circles, or orbits, for electrons are called energy levels. each level can hold only a certain number of electrons. add electrons to each level until you can't add any more. how many electrons can each level hold?

Amale bird-of-paradise uses a dance to attract mates in which it flaps its tail feathers on the ground and jumps around a potential female mate. a different male bird-of-paradise does a similar dance but it jumps around the female in the opposite direction. the female bird is only attracted to one style of dance, in one direction.

How water is moving through the ecosystem ?