A （） in the air delivery line near to each compressor is essential. ["butterfly valve","globe valve","gate valve","non-return valve"]
Anchoring and fishing in this area are（）. ["danger","dangerous","dangerously","dangering"]
当用户使用63010044.png矩形选择工具、63010053.png圆形选择工具选择图像时，在松开鼠标前按下（）可以移动所绘制的图形。 ["Ctrl键","Alt键","Shift键","空格键"]
Adequate attention must be given to the water cooling system of the air compressors, for （） can cause condensation on the cylinder walls. ["overcooling","poor cooling","overloading","unloading"]
在编辑PowerPoint时经常需要更改选定文字的字号，有哪些方法可以更改字号。（） ["单击"增大字号"或"减小字号"","直接在字体工具栏内字号处选定字号","执行"格式"菜单中"字体"命令，弹出对话框，选择相应字体","同时按"Ctrl"+"+"键或"Ctrl"+"-"键"]
混养鱼类品种的选择应掌握哪些原则？
