Simone
一般情况下 be doing是用于做谓语动词，多数情况下是进行时，例如，He is doing his homework.(现在进行时) He was playing computer games at this time yesterday. (过去进行时)当然也有很多特例，例如，He is coming. (现在进行时表将来) 等等而doing一般用于词组，或者常见的主语模猛以及做旦梁桥定语来修饰例如，finish doing, look forward to doing, sth need doing 等等词渣消组中做主语：Eating too much is unhealthy.做宾语：I like jogging. 等等做定语的时候表示主动，例如最简单的 The boy standing under the tree is my friend. (standing under the tree中the boy 和stand 动作关系是主动，用doing 后置做定语)当然还有许多其他例子，例如， There is a girl crying. (There be sb. doing)总之，be doing 可以做句子的谓语成分，而doing不会。I hope this will be helpful to you.
