1. Make a straight line perpendicular to the known straight line and pass through points A and B..

2. It is known that point M on straight line AB and point N outside the straight line connect MN.

Make MN perpendicular to AB

3. Given the straight line and its upper point m, the intersection point m is MN perpendicular to AB.

4. it is impossible to draw the vertical line of the line segment beyond point m.

A.

1

B.2

C.3

D

.4

1, the straight line passing through point A and point B is unique, and it only exists occasionally when it is perpendicular to the known straight line.

2. Same as 1.

The following statement is correct.

B

One of all the line segments connecting a point outside the straight line and a point on the straight line has the longest length.

B a vertical line segment is the shortest of all the line segments connecting a point outside and points on the line.

A point outside the connecting line and a point on the line are the shortest.

In a straight line segment, a point outside the straight line connects with a point on the straight line. One and only one line segment is the shortest.