选B
In the dark street ,there wasn't a single person to whom she could turn for help.
在黑暗的街上,她找不到一个人来帮助她
把to放turn后面就明白了
In the dark street ,there wasn't a single person whom she could turn to for help.
turn to sb.for help.向某人求助
to whom she could turn for help.定语从句,修饰person