drop-in
n.旁聽生
eg. After a while, the drop-in stopped appearing at all, but he would sometimes come around to give the professor advice.
過了一陣子，這位旁聽生不再來了，不過有時會前來給這位教授一些建議。

drop out
(中途)退學；退出
eg. She longed to drop out of the race and make an independent life for herself.
她真想脫離這個圈子去過自由的生活。

biological mother
生母；親生母親
eg. If somebody approaches the tortoise, the hippo becomes aggressive, as if protecting its biological mother," Kahumbu added.
如果有人要靠近老海龜，那么小荷馬就會變得很有攻擊性，就像要保護自己的生母一樣。

unwed
adj. 未婚的
eg. The young, unwed lady is going to have a baby this winter.
那位年輕的且未婚的女士今年冬天就要生了。

pop
vi. 突然出現
eg. The cork popped out and the Champagne gushed from the bottle.
木塞砰的一 聲打開，香檳酒從瓶中溢了出來。

relent
vi. 變得心軟
eg. She relented when she saw her husband bursting into tears.
看見丈夫一哭，她的心就軟了。