Forests help to keep water from running away, _____ drought does not often happen.
A. and
B. but
C. so
D. though
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I am looking for a baby-sitter. she must be _____ too old too_____ young.
A. neither; nor
B. both; and
C. either; or
D. not only; but also
酸性介质中,S2O82–具有强氧化性,当催化剂硝酸银存在时,过二硫酸根可更快的将Mn(II)氧化成( )
酸性介质中,亚硝酸钠分别与KI和KMnO4反应,来考察其( )和( )。
为了验证溶液中有碘单质生成,向溶液中滴加淀粉,溶液会变( )色