为什么图片置入版面后变成了一个带“X斜线”的灰色块？
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当骨料粒径≤31.5mm时，应选用（）mm的混凝土试模成型。
A. 150×150×150
B. 200×200×200
C. 100×100×100
During a period of whiteout，you should expect which of the following（）.
A. Snowfall or blowing snow
B. Lack of ability to estimate distance
C. Harsh contrast between sun-illuminated snow cover and the background
D. Hazy horizons with extensive mirage effect
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