填空题（4.0分）20.Some genetically modified foods, like purple tomatoes, are engineered to contain higher____levels, which may help reduce oxidative stress-related diseases in consumers. (oxygen)第1空fbox(oxygen)

填空题（4.0分） 20.Some genetically modified foods, like purple tomatoes, are engineered to contain higher____levels, which may help reduce oxidative stress-related diseases in consumers. (oxygen) 第1空 $\fbox{oxygen}$