How many types of motors are generally used in the shaver

单项选择题According to the passage, which is the principal energy source of home heat

单项选择题Which of the following countries has the largest share of coal reserves in developing countries

单项选择题According to the Velen model, the middling sort of customers bought luxury goods to______.

单项选择题In the first paragraph, the author mentions McKendrick and Plumb most probably in order to ______.

单项选择题Concerning the answer to who the consumers were, the writer of the passage seems to______.