Why isn't the Sun shrinking or expanding?
A) Because the Sun is spinning so fast, the centrifugal forces keep the surface of the Sun supported against collapse.
B) because gas pressure balances gravity in the Sun
C) because the Sun is solid
D) because the Sun has lived for billions of years
B
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Neutral hydrogen clouds appear ________ when viewed visually
Fill in the blank(s) with correct word
This star map shows stars as we see them in our sky from Earth, centered around the constellation Canis Major. Larger dots represent brighter stars, and a few of the brightest stars are identified. From this view alone, what can you conclude about Sirius?
A) It has the greatest apparent brightness of any star in this region of the sky. B) It is the most luminous star in this region of the sky. C) It is the nearest star in this region of the sky. D) It is actually a binary star system in which the second star is a white dwarf. E) All of the above choices are true.
As an object moves faster through the air, its terminal speed increases
a. True b. False Indicate whether the statement is true or false
Which of the following statements about humoral immunity is correct?
A. It is mounted by lymphocytes that have matured in the thymus. B. It is a form of passive immunity produced by vaccination. C. It defends against free pathogens with effector mechanisms such as neutralization, stimulation of phagocytosis, or complement activation. D. It protects against pathogens that have invaded body cells as well as against cancer cells. E. It requires recognition of class I MHC molecule-antigen complexes to activate its effector mechanism.