Three dimensions, two intersecting planes.
20. AB ⊥ CD? There's a little perpendicularity indicator where they meet so YES
21. EF and CD meet at D. NO
22. D E and F are all on the same line. YES
23. G is in plane N but not plane M, B and E in plane M not N. Three noncollinear points determine a plane, here not M or N. YES
24. Two planes intersect in a line, here that's CD. YES
25. AB ⊥ N ? This is the interesting question. The plane N is formed by two lines, call them HG and HD. Both of those are perpendicular to AB. So every line in the plane N will be perpendicular to AB so plane N is perpendicular to AB. YES
