Denny's parents worried that he might be led ___ by his inappropriate friends.

astray (adv.) 意為「迷途地、誤入歧途地」，lead sb. astray 是固定搭配，指「帶壞某人、使誤入歧途」，完全符合父母擔心孩子被壞朋友帶壞的語境。