At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga.
Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus.
Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.
If B is in between A and C, then AC + AB = BC can't be true because AC is the whole and it is being added to AB which is a part. BC is also a part so it would not make sense if the whole thing plus a part of it is equal to a part. Ex. Say AC is 8, AB is 3, and BC is 5. Putting this numbers in their place would make it 8 + 3 = 5 which is definitely not true.
2. Sometimes true
In a linear pair, the angles have to be adjacent( next to each other). However, in a parallelogram and in a quadrilateral that is inscribed in a circle, that isn't true. It is the opposite angles that are supplementary but they are not adjacent. But two angles that are supplementary can form a linear pair so it is only sometimes true.
3. Always true
The two angles formed by the intersecting lines are congruent and they are adjacent. Knowing that, I can conclude that they are right angles because for them to be congruent they each have to be 90 degrees (180/2 = 90). Perpendicular lines intersect to form right angles so it is always true. There are no exceptions.
*Sorry, I write a lot.