单选题 From the text we learn that Welchi ______.

A、 is a wicked worm causing as many damages as Blaster did
B、 is a program designed by Haley to detect worms like Blaster
C、 is a program intended to fix the infected machines
D、 is a worm meant to defeat the virus with "pings"

【正确答案】 C

【答案解析】这是一道细节题。根据第五段内容可知，Welchi是一种修补电脑程序感染的软件，故答案为C。