【正确答案】 E

【答案解析】The word wary means "cautious of danger," whereas foolhardy means "reckless." Waning sounds like wary, but it means "decreasing in size." Vigilant means "alert to danger," which is a synonym of wary. Likewise, cautious is a synonym of wary. Arbitrary means "unregulated or unreasonable" and is not an antonym of wary.