The phrase "act up" is often used when something isn’t working properly or when someone is misbehaving. For example, if your phone suddenly freezes, you might say, “My phone is acting up again.” It means it's not functioning the way it should. You can also use it for people—especially kids—when they’re being difficult or misbehaving: “The kids were acting up at dinner last night.” 

在口語英語裡，"act up" 主要有兩個常見意思：一是指「（機器、設備）出狀況、鬧問題」，像是 My phone is acting up, I can't send any messages.；二是指「（人，特別是小孩）搗蛋、鬧脾氣」，例如 The kids started to act up when they got bored. 你可以把它想成某個東西或某個人「行為失常」，跟中文說的「不乖」或「怪怪的」很接近。注意它通常用於現在進行式（be acting up），用來強調問題正在發生；若你直接說 It acted up yesterday. 也可以，只是描述過去的狀況。下次電腦又不聽話，就可以說 My computer is acting up again, instead of simply saying it’s broken—聽起來就更道地囉！

"Equip" is a verb that means to provide the necessary tools, gear, or resources for a particular task or purpose. "Equipment" is a noun that refers to the tools or items needed to perform a specific activity. For example, "You need to equip yourself with a helmet before riding a bike," means you should wear or bring the necessary items, and "The equipment for the gym includes weights and machines," refers to the actual tools used in the gym.

「equip」是動詞，意思是「裝備、配備」，而「equipment」是它的名詞形式，表示「設備、器材」。不少學習者會把動詞和名詞搞混：動詞常用被動語態或後接受詞再加 with + 名詞，例如 The soldiers were equipped with night-vision goggles. 名詞「equipment」多半視為不可數，所以通常不用複數形，也不加 a/an，例如 All the camping equipment was packed neatly. 你也可以把兩者放在同一句裡：We need to equip the classroom with better audio equipment. 只要記住「equip = 動作」「equipment = 物品」，就能自然又正確地運用這對單字！

"Maintain" is a verb that means to keep something in good condition, continue something, or take care of something regularly. "Maintenance" is a noun that refers to the act of keeping something in good condition or the work done to take care of something. For example, you maintain a car by taking it for regular maintenance.

在英文裡，maintain 是動詞，maintenance 則是它的名詞形式，兩者常常讓人搞混；簡單來說，maintain 就是「去做維持這件事」，而 maintenance 則是「維持這件事本身」。例如，你可以說 "We need to maintain good relationships."，表示我們需要去維繫良好的關係；要談到實際的維護工作時，就會改用名詞："Regular maintenance of your bike will extend its life."。另外，maintain 也有「主張、聲稱」的意思，如 "She maintains that she was right."。記得動詞 maintain 後面接受詞，名詞 maintenance 前面通常搭配形容詞或放在 of 介系詞後；掌握這個差異，就能更自然地使用這一對單字！