8.7 go on doing/to do
        
        go on to do　做了一件事后，接着做另一件事。
        go on doing　 继续做原来做的事。
        　 After he had finished his maths，he went on to do his physics.
        　 做完数学后，他接着去做物理。
        　 Go on doing the other exercise after you have finished this one.
        　 作完这个练习后，接着做其他的练习
        
        8.8 be afraid doing/to do
        
        be afraid to do　不敢，胆怯去做某事，是主观上的原因不去做，意为怕；
        be afraid of doing　担心出现doing的状况、结果。 doing 是客观上造成的，意为生怕，恐怕。
        
        She was afraid to step further in grass because she was afraid of being bitten by a snake.
        她生怕被蛇咬着，而不敢在草丛中再走一步。
        She was afraid to wake her husband.
        她不敢去叫醒她丈夫。
        She was afraid of waking her husband.
        她生怕吵醒她丈夫。