What is the main subject of the passage（）
A solution to man's food problem.
B. A solution to the population problem.
C. Advantages of soybean.
D. How to develop good eating habits.
以下叙述中错误的是
A. 语句“Dima a, b As Integer”声明了两个整型变量
B. 不能在标准模块中定义Static型变量
C. 窗体层变量必须先声明，后使用
D. 在事件过程或通用过程内定义的变量是局部变量
According to the author, in which decade of the nineteenth century did a steamship first attempt to compete with the transatlantic packets（）
A. The twenties.
B. The thirties.
C. The forties.
D. The fifties.
在Windows中输入英文时，中西文快速切换的组合键是( )。
Alt+Shift
B. Ctrl+空格键
Ctrl+Alt
D. Shift+空格键
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