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发球机从同一高度向正前方依次水平射出两个速度不同的乒乓球（忽略空气的影响）。速度较大的球越过球网，速度较小的球没有越过球网；其原因是(       ) 。

A．{{*HTML*}}<p><img alt="" src="../AttachFilePick.aspx?path=\ExamPaperRes\2018\7\18\823ba3ba58e546ec827732685eb33ffd\e37b91537bb847d0a7737c0804562e26.jpg" style="width: 94px; height: 19px;" /></p>
B．{{*HTML*}}<p><img alt="" src="../AttachFilePick.aspx?path=\ExamPaperRes\2018\7\18\823ba3ba58e546ec827732685eb33ffd\51aeff89dd1f4d70ac68f981f000e220.jpg" style="width: 125px; height: 30px;" /></p>
C．{{*HTML*}}<p><img alt="" src="../AttachFilePick.aspx?path=\ExamPaperRes\2018\7\18\823ba3ba58e546ec827732685eb33ffd\2092f6568b654208ba29fb664230da13.jpg" style="width: 125px; height: 31px;" /></p>
D．{{*HTML*}}<p><img alt="" src="../AttachFilePick.aspx?path=\ExamPaperRes\2018\7\18\823ba3ba58e546ec827732685eb33ffd\7a62a73eeeef4221948feda57f8a8235.jpg" style="width: 130px; height: 27px;" /></p>

A．{{*HTML*}}<p>K_a2(H₂X)的数量级为10^–6</p>
B．{{*HTML*}}<p><img alt="" src="../AttachFilePick.aspx?path=\ExamPaperRes\2018\7\18\823ba3ba58e546ec827732685eb33ffd\d14cfde298d64f938e917e72b28db093.jpg" style="width: 294px; height: 43px;" /></p>
C．{{*HTML*}}<p><img alt="" src="../AttachFilePick.aspx?path=\ExamPaperRes\2018\7\18\823ba3ba58e546ec827732685eb33ffd\8844f0d7913247d7bd7df85cab6fbf83.jpg" style="width: 195px; height: 28px;" /></p>
D．{{*HTML*}}<p><img alt="" src="../AttachFilePick.aspx?path=\ExamPaperRes\2018\7\18\823ba3ba58e546ec827732685eb33ffd\50ccc90ab81a43e78e0c2f5ba14640df.jpg" style="width: 427px; height: 30px;" /></p>