be afraid to do　不敢，膽怯去做某事，是主觀上的原因不去做，意為怕

　　be afraid of doing　擔(dān)心出現(xiàn)doing的狀況、結(jié)果。 doing 是客觀上造成的，意為生怕，恐怕。

　　She was afraid to step further in grass because she was afraid of being bitten by a snake.

　　她生怕被蛇咬著，而不敢在草叢中再走一步。

　　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。