应该选C.
be off to sth表示“奔向某物”.He is off to a new beginning可翻译为：他要去寻找新的开始/他要奔向新的开始.
此题干扰项为D,若要选D,则句子要去掉to,改为He is leaving for a new beginning他要离开了,去寻找新的开始.