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”。
例句
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。