[单选] The reason why more and more of the large merchant vessels are being powered by medium-speed diesel engines is （）.
A . they operate between 150 and 450 rpm B . they are connected to the propeller by gearing C . their smaller size and weight D . they can be connected directly to the propeller without gearing
LED灯具产品研发需解决的问题是什么？
按照实用化验收要求，变电工作票需要全部在系统中通过流程开票。
如何用感官来评价淡水鱼的新鲜度？
在PMS中，变电继电保护及自动装置记录填写完毕后，需要审核后方能归档。
为什么通常选用白鲢生产鱼糜和鱼丸产品？
The reason why more and more of the large merchant vessels are being powered by medium-speed diesel engines is （）.
