因为1

English hates putting 'because' and 'so' in one sentence. Chinese happily does it. 因为 A，所以 B is the tidy pairing, and it is the safe choice for HSK 2 writing. But in real speech, if the result is short and obvious, people just drop 所以: 因为下雨，我不去了. Nobody blinks. One hard rule: 所以 sits before the subject, never after it. 因为下雨，我所以不去了 sounds broken. When someone asks 为什么, you answer with 因为 alone: 为什么不去？因为下雨。 The full paired version shows up in the reading line here: “因为我不喜欢运动，所以这两个我都不喜欢。” ── 《你喜欢看老电影吗？》

Reason first is the default: 因为 A，所以 B. But Chinese also lets you flip it and trail the reason at the end: B，因为 A. That version is pure street speech, and 所以 vanishes completely. Learners trip here because they keep the Chinese word order but drag English 'so' along, producing a stray 所以 or two 因为. Simple rule of thumb: reason first, 所以 welcome. Reason last, 所以 gone. Notice the 了 in 比赛取消了，因为下雨了 — that 了1 stamps the cancellation as a done deal.