根据所给单词的汉语注释或首字母提示，写出各句中所缺单词的正确形式。
1. The teacher c _________ him because he was late for class that day.
2. It is very convenient to use the s _______ during rush hours in Beijing.
3. Early s ______ on the American continent were mostly Europeans.
4. I think we can p _______ our plan at the meeting to be held tomorrow.
