比如说
1 They live five minutes' walk away from their school---------需要用do,因为live是行为动词
-------How far do they live from their school?
2 Their school is five minutes' walk from here?-------不需要用do,因为里面已经有了is这个be动词.
------- How far is their school from here?
总结：有了be动词就没有行为动词,有了行为动词就不能用be动词.