blithe

2. A blithe heart makes a blooming visage.
人逢喜事精神爽.

3. She said "hi" with the blithe assurance of someone who knew how much she'd been missed.
她高興地說瞭聲“嗨”，好像確信大傢非常想念她似的。

4. Suzanne's feelings about food and eating had gone from blithe unconcern to anxiety.
蘇珊娜對飲食的態度已經從無所謂變成瞭焦慮不安。

5. It does so with blithe disregard for best scientific practice.
沒有考慮最科學的做法就輕率地這麼做瞭。