A.90°B.120°C.150°D.180°
A.90° B.120° C.150° D.180°
A.脈沖寬,脈沖前沿極平緩 B.脈沖窄,脈沖前沿極平緩 C.脈沖寬,脈沖前沿較陡 D.脈沖窄,脈沖前沿較陡