问题
选择题
She wrote a month ago, ______ we’ve heard nothing.
A．since when
B．before which
C．since that
D．after which
答案
答案：A
此题答案选A，其中when 相当于 a month ago。若改为 and since then 也不可以。
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She wrote a month ago, ______ we’ve heard nothing.
A．since when
B．before which
C．since that
D．after which
答案：A
此题答案选A，其中when 相当于 a month ago。若改为 and since then 也不可以。
力沿种植体长轴传导到种植体周围的骨组织，以尽量减少种植体承受的侧向力和扭力