单项选择题

Before microbes were discovered it was believed that some diseases were caused by

A．germ-carrying insects.
B．certain strains of bacteria.
C．foul odors released from swamps.
D．slimy creatures living near swamps.
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单项选择题
The word nature (Line 1, Para. 2) is closest in meaning to which of the following
A．Self-sufficiency.
B．Characteristics.
C．Shapes.
D．Speed.
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