The mistake in the locally printed postage stamps was in the （）

单项选择题A postage stamp's value to collectors is raised if （）

A．there are few others like it
B．there are no errors on the stamps
C．a mistake is made in the ,printing
D．both A and C

单项选择题Which of the following statements about labor unions can be concluded based on the information in the passage（）

A．Labor unions reached their peak of power in the 1986's.
B．It. took labor unions many years to improve conditions for workers.
C．The early labor unions failed .because they were not concerned with the well-being of workers.
D．The early labor unions failed because they could not agree on what they wanted to fight for.