结构 be（is+am+are）+动词ing形式
动词-动词ing形式变化规则
1：一般情况下，直接加ing cook-cooking eat-eating
2: 以不发音e结尾的，去e再加ing make -making taste -tasting
3:重读闭音节结尾的，双写末尾的辅音字母 再+ing
get-getting forget-forgetting sit-sitting
skip-skipping shop-shopping stop-stopping
begin-beginning run-running
swim-swimming
句型结构
肯定句 ：主语+be动词+动词ing+其他
they are walking in the park
she is reading in the classroom
否定句：主语+be动词+not+动词ing+其他
they are not / aren't working in the park
she is not /isn't reading in the classroom
一般疑问句：Be动词+主语+动词ing+其他
Are they working in the park?
is she reading in the classroom?
特殊疑问句：特殊疑问句+be动词+动词ing+其他
what are they doing in the park?
who is reading in the classroom
