A．Speculations about gunpowder, flying machines, etc.B．……

单项选择题If refrigerated, USDA eggs will remain good for ______ weeks from the date stamped.

单项选择题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______.