给定一个短文段落，将其中三处语法错误指出并进行修正。


原文：
Even though he was not the smartest student in class, he always work harder than anyone else. John did good on his test last week, but he still practice more if he wants to keep his grades up. Yesterday, he explain his problem to the teacher, who helped him to understand the concept better.
修改后：

1. Even though he was not the smartest student in class, he always worked harder than anyone else.
2. John did well on his test last week, but he still needs to practice more if he wants to keep his grades up.
3. Yesterday, he explained his problem to the teacher, who helped him to understand the concept better.