Student or Learner
I still remember I fell in love with English from a very young age ,because I thought it was such a(n) ______ language ．
A. helpful B. wonderful C. exciting D. car eful
A, B, and C all sound fine to me.
O.K. naroad, you have not said if it is a one choice question or not. If it is, then taking in to account the way that English is taught in the (non-English speaking) world, B is probably the right answer, however to be strictly true to the English language, C is possible, A is also possible, but I doubt very much that it is correct for you. Or your examiners. Sorry, I forgot the comma.
I still remember I fell in love with English from a very young age, because I thought it was such a(n) ______ language．
<capable of eliciting wonder, arouse [one's] wonder e.g., encourage one to want to study English>
<to arouse or stir up (emotions or feelings>
<creating or arousing excitment>
<stimulating interest and discussion>