1
The 2D shape which has one line of symmetry is the trapezium.
Square
A square
An isosceles triangle and a kite have only one line of symmetry.
Septahedron
septahedron
a line
2D shape
It doesn't have any volume (3D) and it's not a line (1D). Thus, it is a 2D shape.
A '2d' ( 2-dimensional) shapoe is a straight line, or a polygon.
Regular polygon with any number of sides, circle, ellipse, isosceles triangle, rectangle, isosceles trapezium, kite, arrowhead.
1D a single line (?) 2D a flat shape 3D a cube