Beginner Level 初级 (chūjí)
The correct answer to this test is A.
A. “所以 (suǒyǐ)” means “so” or “therefore” in Chinese. Because “因为 (yīnwèi)” and “所以 (suǒyǐ)” are compound conjunctions, they are conjoined in a sentence. “因为” leads a causative clause, while “所以” heads a clause of the results.
B. “但是 (dànshì)” means “but,” and it is a transitional conjunction. It is often used together with “虽然 (suīrán),” however sometimes “虽然 (suīrán)” can be omitted.
For example:
(Suīrán) tā hěn cōngmíng, dànshì bú gòu qínfèn.
（虽然）他 很 聪明， 但是 不 够 勤奋。
He is smart, but not diligent.
C. When “就 (jiù)” is used as a conjunction, it is usually put together with “一” to make a compound conjunction. “一 (yī)… 就 (jiù)…” means “as soon as.”
For example:
Wǒ yì chū mén jiù pèngdào Màikè le.
我 一 出 门 就 碰到 麦克 了。
I met Mike as soon as I got out of my house.
D. “才 (cái)” is typically a compound conjunction, meaning “only…” When used in the construction, “只有 (zhíyǒu)…才 (cái)…,” it leads a conditional and results clause. Sometimes “只有 (zhíyǒu)” can be omitted.
For example:
Zhíyǒu nǔlì cái yǒu shōuhuò.
（只有）努力才 有 收获。
Only one who works hard may succeed.
Both of them are transitional conjunctions. They can be exchanged with each other in most cases.
I learned another phrase “但” in other Mandarin lessons, which also indicates a transition of the meaning. Is it the same as “但是” in this test?
Chinese grammar is different from English in using the conjunction words. We only use a single phrase, but in Chinese, you are used to using compound conjunctions.