【单选题】国际电工标准委员会(IEC)规定了直流安全电压的上限值为()V。
【多选题】我国及 IEC (国际电工委员会)都对安全电压的上限值进行了规定,即工频下安全电压的上限值为( ) V ,其电压等级有 42V 、 36V 、( ) V 、12 V 、( ) V 。同时规定:高度不足 2.5M 的照明装置、机床局部照明灯具、移动行灯等,其安全电压可采用( ) V 为安全电压。
【简答题】在△ABC中,已知a+b=12,∠A=60°,∠B=45°,求a,b。
【单选题】国际电工委员会(IEC)标准规定,工频安全电压的限定值也为()V。
【单选题】Which of the following accurately describes a major difference between a monopolist and firms in perfectly competitive markets?
A.
The monopolist maximizes profit; firms in perfectly competitive markets maximize sales.
B.
The monopolist may earn long-run economic profit; firms in perfectly competitive markets cannot.
C.
The monopolist is a price taker; firms in other markets are price searchers.
D.
The monopolist may earn short-run profit; firms in perfectly competitive markets cannot.
【单选题】Price discrimination by a monopolist is less effective if the
B.
good has no substitutes.
C.
monopolist can identify buyers by willingness to pay.
D.
good cannot be resold.
【简答题】已知在△ABC中,∠A=60°,∠B=75°,AB= 6 ,则BC=______.
【单选题】A major difference between a single-price monopolist and a perfectly competitive firm is that the
A.
monopolist can maximize profit by setting the price of the output where demand is inelastic.
B.
monopolist can always increase its profits by increasing the price of its output.
C.
monopolist's marginal revenue is less than price.
D.
monopolist is guaranteed to earn an economic profit.