单词拼写（15分）
1. Since 1965, the m_________ leaf has been the centerpiece of the National Flag of Canada.
2. When the white liquid was m ________ with water, it became blue at once.
3. Wal-Mart has many chain stores all over the world and you may find one w______ a short walk along a busy street in any big city.
4. There are seven c ______ in the world, of which Asia is the largest.
