e 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.