问题
选择题
.______ the beginning of the 19th century did scientists know that all matter is made up of 
atoms.
A．At
B．By
C．Up to
D．Not until
答案
答案：D
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.______ the beginning of the 19th century did scientists know that all matter is made up of atoms.
A．At
B．By
C．Up to
D．Not until
答案：D