单项选择题

Which of the following is NOT an example of artificial selection

A．the selection by a farmer of the best milk-producing cows for breeding
B．a breeder's allowing only the fastest horses to reproduce
C．the selection for reproduction of the best egg-laying chickens by the farmer
D．an increase in the number of giraffes with long necks because of a decline in the number of low-lying plants used for feeding
<上一题 目录 下一题>
热门 试题

单项选择题
What relationship exists between rail and inland water transport
A．Labor restrictions prevent the two from handling the same traffic and have prevented competition from developing.
B．Railroads carry different commodities and thus are not in direct competition with water transport.
C．They sometimes compete with one another.
D．Railroads are never routed along the same routes as water transport, so the two do not compete.
单项选择题
Why it is difficult to say exactly how many miles of improved waterways are in operation
A．The most recent figure is for 1975 and the figure is declining.
B．Water transport's market share goes up and down frequently.
C．So few miles of inland waterways exist that no one has bothered to count them.
D．You must know whether to include coastwise and inter-coastal shipping in the figure.
相关试题