4的平方根是( )
A.±16
B.16
C.±2
D.2
答案:C
∵(±2)2=4,
∴4的平方根是±2.
故选C
病人表现为双足各种深、浅感觉均受累,常局限于肢体末端,呈手套或袜套状,其神经病变部位应当在()
A.神经末梢
B.神经干
C.神经丛
D.神经根
E.传导束
I ____ to reach the manager for the last two hours but the line is always busy. [ ]
A. tired
B. have tired
C. had tired
D. have been trying