主语+be动词（am,is,are）+动词现在分词（doing）
i'm watching TV.
they are watching TV.
he is playing.
we are cleaning the room.
she is doing her homework.
主语+be动词（am,is,are）+动词现在分词（doing）
i'm watching TV.
they are watching TV.
he is playing.
we are cleaning the room.
she is doing her homework.