①C→CO→CO2②Cu→CuO→CuSO4 ③CaCO3→CaO→Ca(OH)2④Na2CO3→NaCl→NaNO3.
A:①②④
B:①②③
C:①③④
D:①②③④
⑴____ A. grade B. able C. skate D. any
⑵____ A. egg B. me C. went D. tell
⑶____ A. rich B. sister C. swim D. write
⑷____ A. idea B. Korea C. real D. great
⑸____ A. school B. machine C. chemical D. ache
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