I'm going to school by subway. 我乘地铁去上学.
改为否定句：I‘m not going to school by subway.我不乘地铁去上学.

Mom is going to buy some food tomorrow. 妈妈将在明天买一些食物.
改为一般疑问句：Is mom going to buy any food tomorrow? 妈妈将在明天买一些食物吗?