The angle between skew back of a flat arch and the horizontal, is kept approximately equal to

The angle between skew back of a flat arch and the horizontal, is kept

1.	The angle between skew back of a flat arch and the horizontal, is kept approximately equal to
A.	0¬∞
B.	30¬∞
C.	60¬∞
D.	90¬∞
Answer» D. 90¬∞