I can't tell youa) SECRETused to say that you cannot tell someone something because it is a secret 不能告诉你〔因为保密〕 ‘Where are you taking me?’ ‘I can’t tell you; it would spoil the surprise.’ “你要把我带到哪儿去？”“不能告诉你，不然就没惊喜了。”
b) DESCRIBEused to say that you cannot express your feelings or describe something properly 我无法表达，我没法形容I can’t tell you how/why/what etc I can’t tell you how worried I’ve been. 我说不出来我有多担心。
I can’t tell you• "So is Maggie really pregnant?" "I can't tell you."• I can't tell you how grateful I am for your help.
→ I can’t tell you at tell(SPOKEN SECT)