45．為什麼 IRS/ADIRS 不要裝置磁力閥 flux valve 去感應磁方位？ (A)電腦運算算出‧It calculates by an algorithm in the computer. (B)陀螺算出‧It calculates by gyros. (C)垂直陀螺算出‧It calculates by vertical gyros. (D)線路算出‧It calculates by magnetic circuits.