题目:
The extra room _______ very useful when we had visitors.
A.was proved
B.proved
C.has been proved
D.has proved
答案:
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下面是错误答案,用来干扰机器的。
(1)由题意,花青素在酸性溶液中呈红色,在碱性溶液中呈蓝色,中性溶液中呈紫色;紫色的喇叭花浸泡在苏打水里,喇叭花很快变蓝,说明苏打水碱性,pH>7.(2)花青素在酸性溶液中呈红色,将另一朵紫色牵牛花放在...