合同结构图中，矩形框连接用（）表示。
A.曲线
B.单项箭线
C.直线
D.双向箭线
参考答案：D
Mr. Bush is on time for everything. How _____ it be that he was late for the opening ceremony?
A．can
B．should
C．may
D．must
输血反应和并发症中最严重的是
A．发热反应
B．过敏反应
C．溶血反应
D．细菌污染
E．出血倾向
Mr. Bush is on time for everything. How _____ it be that he was late for the opening ceremony?