Translation:We ask the doctor.
让我们问医生。is "Let's ask the doctor" or "Let us ask the doctor." That first character, 让 , is pronounced rang4, and means basically "let's" or "let us." (It has other, related meanings, such as to ask, to let, to permit, to yield, to allow, or to have someone do something, but "let's" or "let us" is the meaning you are asking about.)
Perhaps a little more casually, 让我们问医生，好吧？means basically, "How about (if) we ask the doctor?" or "Let's ask a doctor, okay?" The 吧 at the end of the sentence is typically pronounced ba (ba5, the neutral tone), and is a modal or interrogative particle indicating polite suggestion, such as "right?" or "okay?" in English.
@wojtek - you need to rewrite your entire comment like this - "..having to repeat exercise because I skipped 'the' is highly annoying.." + "..which is intended meaning of sentence." I hope you noticed what I noticed. You inadvertently added a few "the"s yourself without realising (the) fact. :-)
We ask the doctor requires an object. Let us ask the doctor is better English. If you want your students to learn proper grammar in Chinese, then the appropriate gramatically correct English translation should be used. Orherwise, it sounds like gibberish that you are teaching us.