不好说。(Bù hǎo shuō.)It's hard to tell.

用法说明
“不好说”这句话表示“不确定,不能轻易地下结论或给出确切的答案”, 可以单独使用,也可以用在句末,形成“……不好说”的结构,前边一般是有疑问的内容。还可以说 “难说”或者“说不好”。
Meaning:
This sentence means "It's difficult to make a conclusion or to give definite answer." It can be used alone as a sentence, or in the pattern "……不好说。" You can also say "难说(nán shuō)" or "说不好(shuō bu hǎo)" to express the same meaning.

例句
sentences
1、Jiǎ:Qǐnɡwèn,Wánɡ lǎoshī shénme shíhou huí lɑi?
甲:请问,王老师什么时候回来?
A: Could you tell me when teacher Wang will come back?
Yǐ:Bù hǎo shuō,nǐ mínɡtiān zài dǎ yí cì diànhuà bɑ.
乙:不好说,你明天再打一次电话吧。
B: I can't give you an exact answer. Please try again tomorrow.

2、Jiǎ:Yīshēnɡ,wǒ zhànɡfu zěnmeyànɡ le?
甲:医生,我丈夫怎么样了?
A: Doctor, how is my husband now?
Yǐ:Yǐjīng tuōlí wēixiǎn le, dànshì nénɡbunénɡ huīfù jiù bù hǎo shuō le.
乙:已经脱离危险了,但是能不能恢复就不好说了。
B: He is free from danger now, but it's difficult to tell whether he can recover or not. 

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