That would be two sopranoes and one bass. So the answer is B
Post-and-lintel system
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Post-and-lintel system, in building construction, a system in which two upright members, the posts, hold up a third member, the lintel, laid horizontally across their top surfaces. All structural openings have evolved from this system, which is seen in pure form only in colonnades and in framed structures, because the posts of doors, windows, ceilings, and roofs normally form part of the wall.
Answer:
One World Trade Center (WTC 1, or the North Tower) was hit at 8:46 a.m. Eastern time and collapsed at 10:28 a.m. Two World Trade Center (WTC 2, or the South Tower) was hit at 9:03 a.m. and collapsed at 9:59 a.m.
How long did it take for the south tower to collapse?
56 minutes
9:57: The passengers aboard Flight 93 begin a revolt against the hijackers in an attempt to take back the plane. 9:59:00: The South Tower of the World Trade Center collapses, 56 minutes after the impact of Flight 175.
