A、<span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-ascii-font-family: ">流速有方向,作用力没有方向</span>
B、<span style="FONT-FAMILY: ; FONT-SIZE: 10.5pt"><span style="mso-spacerun: yes"></span></span><span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-ascii-font-family: ">流速没有方向,作用力有方向</span>
C、<span style="FONT-FAMILY: ; FONT-SIZE: 10.5pt"><span style="mso-spacerun: yes"></span></span><span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-ascii-font-family: ">都没有方向</span>
D、<span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-ascii-font-family: ">都有方向</span>
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