b?我看了一下，楼上两位说得也很对，我刚才忘记了伴随状语的用法，的确，当伴随状语来形容一件事或一个人时，确实不需要用be动词，刚才是我不对，抱歉了！ 至于动名词作主语的问题，我想一个最简单的办法就是看这个整句里谓语上有没有动词出现，比如说： having a balanced diet is very important. 此句中，谓语上有be动词出现，要用动名词作主语，当然也可以写成： to have a balanced diet is very important. 而在祈使句中就不要用，例如： shut the door ,please. 此句中谓语上没有动词的出现，所以就不要用。 以上全是个人总结，仅供楼主参考，如果楼主还有不会的，请发短信问我，谢谢！

动名词做主语造句 一、谓语用单数 Swimming is good to me. Doing homework makes me unhappy. Planting trees makes our environment better. Watching too much TV does harm to our eyes. Reading books is my hobby. 例：-What do you think made Mary so upset？-___ her new bicycle. A. As she lostB．Lost C．Losing D．Because of losing 二、 使用形式主语it，而将动名词放在句尾。 It’s a waste of time doing … It’s no good doing… It’s no use doing … 例：It’s no good______ (wait) here. It’s no use ______(argue) with her. It’s no good _______(smoke), you’d better give it up. It’s a waste of time _______(wait) here.