1. They will meet at the gate _______.(tomorrow morning, on tomorrow morning)
2.They often play football _______.(this afternoon,in this afternoon)
3.David goes to school _______.(on foot,by a bus, take a bike)
4.I'll visit my grandparents _____.(in five days,aften five days)
5.We'll go camping ______.(next week,in next week)
最好可以说明原因..
參考答案:1. 参考答案为tomorrow morning, 如果把morning去掉，你就很自然的知道不用介词了，morning修饰tomorrow的。
2. 应该说两个都是不恰当的，因为句中often表示频率，而this表特指。要么把in this afternoon 改为in the afternoon，要么把often去掉，选用 this afternoon
3. 参考答案为on foot，是固定搭配。by bus 而不是by a bus，是ride a bike而不是take a bike
4. 参考答案为in five days，in 后加一时间段表示多久以后。句子意思是，五天以后我回去看我的祖母。after一般不用在将来时中。
5. next week，解释参见第一题。
