单项选择题
A．his wife’s encouragement B．a lot of money to buy equipment C．engineers and technicians D．to produce a gasoline engine that would be the power for his car
A．no plants would grow on our planet B．earth would be thirty degrees colder C．man could not live on the earth D．all of the above answers are correct
A．the way in which gases are used for keeping plants warm B．a natural course which is to some degree helpful to us C．the way" greenhouse gases trap heat on the earth D．the whole course in which greenhouse gases prevent heat