选D.
Even as a girl,【Melissa knew that performing was】to be her life, and theater audiences were to be her best teachers.
翻译:
还是个女孩的时候/仍在孩提时期,Melissa就知道表演将会成为她的生命,剧院的观众们也会成为她最好的老师。
答案是D。空白处需要找到有人称作主语的选项,而且后有and连接,前边需要句子而不是A或C这样的非谓语形式。“即使是女孩,Melissa也知道表演将会是她的生命而且剧场观众...”