题目

Parents whose children show a special interest in a sport feel very difficult to make a decision about their children’s careers. Should they allow their children to train to become top sports men or women? For many children it means starting schoolwork very young, and going out with friends and other interests have to take a second place. It’s very difficult to explain to a young child why he or she has to train five hours a day, even at the weekend, when most of his or her friends are playing. Another problem is of course money. In many countries money for training is available from gover5．焦点为F的抛物线C：y2=8x的准线与x轴交于点A，点M在抛物线C上，则当$\frac{{|{MA}|}}{{|{MF}|}}$取得最大值时，直线MA的方程为（　　）A．y=x+2或y=-x-2B．y=x+2C．y=2x+2或y=-2x+2D．y=-2x+2