单选题 It's said that the agreement ______ between the two companies last month will become effective from May 1st.
   A) to sign           B) signed        C) to be signed   D) signing
【正确答案】 B
【答案解析】通过句中的last month我们可以判定sign的动作发生在过去，signed这个过去分词做定语修饰主语。