Stable interest rates on long-term bonds are the financial market's vote of confidence in the Federal Reserve keeping in control of inflation. (A) in the Federal Reserve keeping in control of inflation (B) that the Federal Reserve will keep inflation under control (C) for the Federal Reserve, that it would keep control of inflation (D) that inflation will be kept control of by the Federal Reserve (E) that inflation would be kept control of by the Federal Reserve
A is wordy, confidence in ... keeping in control of ... C confidence for..... is unidiom, and that clause has no object. Also, the tense of would is wrong. D and E use unidiom structure, be kept control of by...., and compared with B, passive voice is not recommended as well.
BTW, in B, that clause is appositive clause of confidence.