The types of living organisms on Earth have changed over time-new species have originated and existing species have disappeared. This is an example of
A. speciation.
B. extinction.
C. macroevolution.
D. alternation of generations.
E. hybridization.
C. macroevolution.
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Among couples using a method of birth control consistently and correctly, the most important determinant of pregnancy risk is ______.
[A] their marital status [B] their ethnic or racial group [C] their income group [D] their frequency of sex
The structure indicated by the letter "B" above represents _____
a. actin b. a myofibril c. myosin d. the sarcoplasmic reticulum e. a muscle fiber
A flap of tissue called the __________ directs air through the __________, the opening to the
__________ (windpipe). Fill in the blank(s) with the appropriate word(s).
Which structure prevents food from traveling down the trachea?
A) Pharynx B) Bronchus C) Glottis D) Epiglottis