“发小苗不发老苗”的土壤质地是（）。
A.沙土
B.壤土
C.粘土
D.都不是
参考答案：A
The basic causes are unknown although certain conditions that may lead to cancer have been ().
A. identified
B. guaranteed
C. conveyed
D. notified
汽轮机起动升速和空负荷时，为什么排汽温度反而比正常运行时高？采取什么措施降低排汽温度？
