严峻的

In this context, '严峻的' (yánjùnde) means 'severe' or 'grim,' which fits the idea of a challenge that requires unity. '轻松的' (qīngsōngde) means 'easy,' '愉快的' (yúkuàide) means 'pleasant,' and '简单的' (jiǎndānde) means 'simple,' none of which are appropriate here.

Here, '严峻' (yánjùn) is used to describe a 'grim' or 'severe' economic situation, implying a need for preparation. '光明' (guāngmíng) means 'bright,' '乐观' (lèguān) means 'optimistic,' and '开朗' (kāilǎng) means 'outgoing' or 'cheerful,' none of which fit the context of needing to be prepared for a difficult situation.

'严峻' (yánjùn) is used here to describe 'severe' or 'harsh' weather, which would cause significant difficulties for rescue efforts. '晴朗' (qínglǎng) means 'sunny,' '温和' (wēnhé) means 'mild,' and '凉爽' (liángshuǎng) means 'cool,' none of which would typically create '巨大困难' (jùdà kùnnán, great difficulties) for rescue work.

While '严峻的' (yánjùnde) can describe challenges, when talking about 'his attitude' (他的态度), '积极的' (jījíde, positive/active) is the most fitting word to describe how someone would face challenges, implying resilience or determination. '消极的' (xiāojíde) means 'negative' or 'passive,' and '轻松的' (qīngsōngde) means 'relaxed' or 'easygoing,' which are less appropriate in this context.

Here, '严峻' (yánjùn) refers to a 'strict' or 'tight' deadline, which necessitates working quickly. '宽裕' (kuānyù) means 'ample' or 'generous,' '弹性' (tánxìng) means 'flexible,' and '灵活' (línghuó) means 'flexible,' all of which contradict the idea of needing to '抓紧时间' (zhuājǐn shíjiān, seize the time/work quickly).

In this sentence, '严峻的' (yánjùnde) accurately describes 'global warming' as a 'severe' or 'grim' issue that demands international cooperation. '微不足道的' (wēibùzúdào de) means 'insignificant,' '次要的' (cìyàode) means 'secondary,' and '简单的' (jiǎndānde) means 'simple,' none of which would necessitate international cooperation for resolution.