单项选择题

Lighting levels are carefully controlled to fall within an acceptable level for optimal reading convenience.

A．ideal
B．required
C．optional
D．standard
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单项选择题
An international treaty signed several years ago bans trade in plants and animal of endangered species.
A．forbids
B．eliminates
C．promotes
D．protects
单项选择题
A good employer gives hints to his or her employees without interfering with their creativity.
A．freedom
B．assistance
C．clues
D．funds
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