题干
Great changes ______ in our hometown in the past five years.
A：happened
B：have happened
C：were taken place
D：happen
答案(点此获取答案解析）
B
Great changes ______ in our hometown in the past five years.
A：happened
B：have happened
C：were taken place
D：happen
发现有白色沉淀生成，继续滴加则沉淀消失，将丁溶液滴入甲溶液时，无
明显现象发生，据此可推断丙物质是