(Q).
Q: What events, resulting in death of over half of animal species, have occurred on earth at least five times in the past 540 million years? Choices: - mass migrations - microevolutions - spontaneous mutations - mass extinctions A:
(A).
mass extinctions

(Q).
Q: In essence, a virus is simply a nucleic acid surrounded by what? Choices: - a membrane coat - a polymer coat - a polypeptide - a protein coat A:
(A).
a protein coat

(Q).
Q: What is the term for an ionic compound that produces positive hydrogen ions when dissolved in water? Choices: - hydrocarbon - sulfur - base - acid A:
(A).
acid