未知题型 New governmental______on food were enforced to prevent the spread of the bacteria to consumers.A．tiesB．actsC．bordersD．restrictions

未知题型 Vacation requests must be made at least one month prior to the______date.A．wantedB．desiredC．electedD．established

单项选择题 冲洗水箱的种类较多，按冲洗的水力原理分为（ ）。 A．延时自闭式 B．冲洗式和虹吸式 C．手动式和自动式 D．高水箱和低水箱