[填空题] 在渠道控制中，最直接最明确的控制方式是（）。

（） are used for cargo handling. ["Cranes","Mooring winches","Windlasses","Forema"] The conclusion is（）the said ship is fit to continue to sail. ["it","this","that","what"] 简述纤毛虫病。 一个生态演替的顶级群落的典型特征是（）。 ["生态系统相对稳定","生物量的增长达到最大","植物与动物的物种数量持续快速增长","每一年的生态系统净生产量都不同"] In a hydraulic system, （） are used to protect the system from over pressure. ["stop valves","check valves","safety valves","reducing valve"] 在渠道控制中，最直接最明确的控制方式是（）。