Given the following example code, which overrides are valid and which one aren't (with explanation)?

Description:

private abstract static class C1 {
public abstract void m1() throws Exception;
public abstract void m2() throws IOException;
public abstract void m3() throws Exception;
}
private static class C2 extends C1 {
@Override
public void m1() throws IOException {}
@Override
public void m2() throws Exception {}
@Override
public void m3() {}
}

Solution: