立地级法是采用林分（）高评价立地质量的方法。
参考答案：标准年龄时林分平均
The students were ________ over the ________ problem，listening to the teacher with a ________ expression on their faces.
A．puzzled；puzzling；puzzling
B．puzzled；puzzling；puzzled
C．puzzling；puzzling；puzzled
D．puzzling；puzzled；puzzling
干细胞
