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Average cattle size over the past 100 years has increased steadily. Cows, on average, are more than 100
pounds heavier than they were a century ago. What is the most likely explanation of the increases observed in
the cows?
A
B
C
D
Increased global temperatures have decreased disease incidence of the cattle, leading to their
increased growth.
Increased water availability as water levels rise increased the growth and mass of the cattle.
Decreased competition with other mammal species in the wild has increased the aver-age growth rate
of cattle.
Humans have bred the cattle to have improved genetics that increase growth rates and mass.
N
