Weddings can be seen, but love can't be seen; love letters can be seen, misses can't be seen, flowers can be seen, spring can't be seen; fruits can be seen, nutrition can't be seen; the action of help can be seen, caring can't be seen; blowing wind can be felt, the air is invisible; the diploma is visible, but the level is invisible
Some people have come to the conclusion that the invisible is more valuable than the visible
There are three types of triangles: right-angled triangles, obtuse-angled triangles, and acute-angled triangles. The sum of the interior angles of a right triangle is 180°, the sum of the interior angles of an obtuse triangle is 180°, and the sum of the interior angles of an acute triangle is 180°, so the sum of the angles of all triangles is 180°.