单项选择题
A．planes fly higher than at the equator B．the eyes can reach about 4,000 meters C．planes are clear of bad weather D．planes fly more quickly than at the equator
A．say B．describe C．mention D．write
A．New trees are not looked after properly. B．Many trees have been cut down by man. C．Man has not paid enough attention to planting trees. D．All of the abov