做此类题目,个人建议你现将句子变成一般疑问句；然后再对划线部分提问,效果会更好.
1、一般疑问句：Do the students want to go to Mr Smith's farm for a picnic?
2、对应划线部分,找好相应的特殊疑问词,然后将一般疑问句置于特殊疑问词之后,再将划线部分去掉即可.
Where do the students want to go for a picnic?