There are 3 birds standing in the tree. There is a book openning on the desk. There are some children playing in the river. 这个是there be的句型,后面用现在分词做后置定语.
There are a lot of farmers working in the fields. There are 3 girls singing English songs. There is a boy cleaning the classroom. 句型是There be +主语+doing sth. +其他.。