标定NaOH溶液的基准物质有草酸和无水Na2CO3（）
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According to the passage，a life be first of all（）
A. adjustable
B. comf ortable
C. self -evident
D. selfrighting
United States Coast Guard does NOT require the life preserver to bemade_
A. with as few strings as possible
B. capable of being worn on both sides
C. according to each wearer s size
D. confortable and light to we ar
洗涤沉淀是为了洗去表面吸附的杂质及混杂在沉淀中的母液（）
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