输入端一般接开关，输出端接LED灯，对吗？
A. 对
B. 错
输入端有圆圈表示什么，输出端有圆圈表示什么？
A. 输入端有圆圈表示低电平有效，输出端有圆圈表示取反
B. 输入端有圆圈表示取反，输出端有圆圈表示低电平有效
To many businesspeople, one of the major attractions of a sole proprietorship is
A. the ability to obtain additional financial resources.
B. the protection of limited liability.
C. an unlimited lifespan.
D. the chance to be their own boss.
The ________ is the most common form of business ownership.
A. partnership
B. corporation
C. joint venture
D. sole proprietorship
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