三面投影体系中，W面展平的方向是（  ）。

A、<span style="FONT-FAMILY: 宋体; BACKGROUND: white; FONT-SIZE: 14px">W</span><span style="FONT-FAMILY: 宋体; BACKGROUND: white; FONT-SIZE: 14px">面永不动&nbsp; </span>

B、<span style="FONT-FAMILY: 宋体; BACKGROUND: white; FONT-SIZE: 14px">W</span><span style="FONT-FAMILY: 宋体; BACKGROUND: white; FONT-SIZE: 14px">面绕Z轴向左转90°</span>

C、<span style="BACKGROUND: white; FONT-SIZE: 14px; TEXT-DECORATION: none">W面绕Z轴向右转90°&nbsp;</span>