单项选择题
A．如果发动机长时问不能工作，我们建议要采取措施以防止发动机锈蚀。
B．如果发动机要长时间停机，我们建议采取以下措施以防止发动机生锈。
C．如果发动机经常出现故障，我们认为应该立即检查发动机是否已生锈。
D．如果发动机维修的时问长，我们认为应该立即对其生锈部分采取措施。
单项选择题 As is known to all, trade and specialization go hand in hand and enable each of us to have more products to use（）
单项选择题 We will offer you a 20 percent discount if you are among the first fifteen customers of the day（）
单项选择题 If we（）more time and money, we could have visited many more places.