on one's guard

A black-browed barbet, one of Taiwan's endemic birds, stands guard by its nest in a tree on a street in Taipei.

一只台湾独有的黑眉巨嘴鸟正在台北的街边树上保卫自己的巢。

Feeling that all extremes meet, and that, if one is not on one's guard, lowered fortunes may lead to baseness of soul, he kept a jealous watch on his pride.

他感到人间事物是一一相承，物质的缺乏可以导致灵魂的堕落，于是便疾恶如仇捍卫着自己的自尊心。

Japan's coast guard plucked a stranded Chinese balloonist out of the sea near the disputed Senkaku Islands on New Year's day after the man tried and failed to land on one of the islands.

日本海上保安厅元旦在有争议的尖阁诸岛（Senkaku Islands，中国称这些岛屿为钓鱼岛及其附属岛屿）附近海域救起了一名落水的中国热气球驾驶者。此人曾试图降落到其中的一个岛屿，但没有成功。