The Width of an Expansion Joint Between Adjacent Mullion Lengths

The width of an expansion joint between adjacent mullion lengths in a typical stick- built glass curtain wall

A) is generally 1/2 in. standard.
B) is generally 1 in. standard.
C) is generally 1/16 in. standard.
D) is generally 1/4 in. standard.
E) must be determined on a project- by- project basis.