我国竖炉与国外相比有什么显著特点？
参考答案：
烘干床，导风墙。
两个单数无论是相加或相减（大数减小数），结果一定是双数。[ ]
—_______ have you been learning English?
—So far, more than 10 years. [ ]
A. How often
B. How long
C. How many
D. How far
