Lung cancer, like some other cancers, often doesn‘t produce _____ until it is too late and has spread beyond the chest to the brain, liver or bones.
句意： 肺癌， 和其它癌症一样， 通常到晚期才会出现症状， 而这时癌细胞已经扩散至大脑、 肝脏、 骨髓。 symptoms症状。 trials痕迹。 therapy治疗法。symbol象征。 本题答案为C。