Now someone modifies the definition and give the following alternative one:
Def 2.
A tree consists of a root, and one or more subtrees T₁, T₂,..., T_k. Also, there is an edge from the root to the root of each subtree.
Can you describe what will happen if we choose the second one as the definition instead? What trees can be generated by the two definitions?

Def 1.
A tree consists of a root, and zero or more subtrees T₁, T₂, ..., T_k. Also, there is an edge from the root to the rootof each subtree.

6. [15%] Which of the following graphs, K₆ (complete graph with 6 vertices) or K₇ (complete graph with 7 vertices) has closed Euler walk? Explain your answer as clear as possible. That is, in closed Euler walk, we allow each edge to be visited exactly once, and the initial vertex and ending vertex are the same. Can we modify the graph(s) to make it/them possible to contain a closed Euler walk?

50. 在鏡頭的特性中，「景深」(Depth of Field )一詞指的是： (A) 底片或感光元件上形成清晰影像的景物深度 (B) 是指畫面的色彩深淺程度 (C) 底片或感光元件上形成影像的大小範圍 (D) 是指被攝物與鏡頭的距離

49. 下列關於「確定鏡頭」(Establish Shot)的敘述，何者正確？ (A) 表現主角遇到某件事的表情或動作 (B) 通常在影片的開始片段，會先建立場景環境的樣貌 (C) 將影片中某一個人的視角以攝影機取代 (D) 鏡頭除了背景之外，特別聚焦在一個人物取鏡

48. 攝影時可採用「背光」勾勒出被攝者身形的「輪廓光」。但若背光過強，被攝者的身形可能 出現何種效果？ (A) 剪影效果 (B) 閃光燈效果 (C) 煙霧效果 (D) 多重色彩效果