The tension in the cord occurs because of the muscle power of Daryl, who lifts the brick. While doing so, Daryl needs to overcome the gravitational pull on the brick.
EXTRA:
If the brick was much heavier, than Daryl's muscles would not be able to overcome the the gravitational pull on that brick, and then the much heavier brick would remain stationary on the ground, despite the efforts made by Daryl.
A line of symmetry is a line that separates a shape into two identical halves. Rotational symmetry is the same thing except when you rotate the object, it has to have the exact same line of symmetry.
