(2013·安徽蚌埠第一次质检)Finding information in today's world is easy. The ________ is how you can tell if the information you get is useful or not.

A．knowledge

B．ability

C．competition

D．challenge

对嗜铬细胞瘤的临床表现，以下说法正确的是

A．可有体位性低血压

B．表现为阵发性高血压或持续性高血压基础上有波动

C．发作时可伴心律失常

D．酚妥拉明试验阳性有助于诊断