小小解说员（解释词语）。

1．束手无策：                                                                                                                                 

2．垂头丧气：                                                                                                                                 

3．胸有成竹：                                                                                                                                 

节细胞神经瘤的描述中，错误的是（）

A.发病年龄高于神经母细胞瘤

B.肿瘤不规则，无包膜

C.切面灰白或灰黄，常见钙化点

D.可见成熟神经节细胞、神经纤维和纤维组织

E.临床症状不明显