第1个回答 2011-08-02
Two birds are singing in the tree.(现在进行时)
Two birds were singing in the tree.(过去进行时)
第2个回答 2011-08-02
Two birds are singing in the tree.(现在进行时)
Two birds were singing in the tree.(过去进行时)
第3个回答 2011-08-02
There are two birds singing on the tree.
第4个回答 2011-08-02
Two birds are singing in the tree.本回答被网友采纳