What does Bill ask Frank to do before he takes his leave?
Ask Lisa to help with his project.
B. Present a detailed progress report.
C. See his mother immediately.
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1、与继电控制及一般的计算机控制相比较，可编程控制器有什么特点？
Listen to the conversation and choose the reasons Frank puts forward in their talk.[音频]
A. His headache
B. His stress
C. His bad sleep
D. His heart disease
E. His sick mother
关于光电效应的截止电压,下列说法不正确的是:（ ）
A. 光电管的阳极反向电流、暗电流、本底电流会影响截止电压的测量。
B. 测量截止电压时，一般有零电流法、补偿法和拐点法。
C. 对于不同频率的光，其截止电压值是相同的。
D. 光电流慢慢减小直到为零时的反向电压称为截止电压。
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