Answer:
Bottom line: There's no eclipse at every full moon and new moon because the moon's orbit is inclined to Earth's orbit by about five degrees. Most of the time, the sun, Earth and moon don't line up precisely enough to cause an eclipse
Explanation:
A lunar eclipse occurs when the Moon enters the Earth's shadow. A solar eclipse occurs when the Moon's shadow falls on the Earth. They do not happen every month because the Earth's orbit around the sun is not in the same plane as the Moon's orbit around the Earth.
Answer:
The immune system responds to antigens by producing cells that directly attack the pathogen, or by producing special proteins called antibodies.
Explanation:
Specific immune responses are triggered by antigens. Antigens are usually found on the surface of pathogens and are unique to that particular pathogen. The immune system responds to antigens by producing cells that directly attack the pathogen, or by producing special proteins called antibodies.
The immune system review (article) | Khan Academy
Answer:
1) Recursive definition: 
2) At the beginning of the 4th interval
Explanation:
1)
The initial population of the bacteria at time zero is
Here we are told that the reading is taken every two hours; we call this time interval "n", so
And also, after every time interval n, the number of bacteria has tripled.
This means that when n = 1,
And when n=2,
Applied recursively, we get
And substituting p0,
(1)
2)
Here we want to find at the beginning of which interval there are
bacteria.
This means that we can rewrite eq.(1) as
By simplifying,
Which means that
However, this means that the number of bacteria is 1,350,000 after 3 time intervals; therefore, at the beginning of the 4th interval.
