解释下列词语  

①嘱咐：                                      

②坦然：                                      

③倔强：                                      

④沮丧：                                      

⑤恍惚：                                      

⑥嗫嚅：                                      

⑦伤感：                                      

⑧抱怨：                                    

二叉树（BinaryTree）