Teenagers have different opinions about homework. Some think it is necessary for learning. Others believe it is a waste of time. A survey asked 50 teenagers about their opinion. The table shows the results of the survey.
| Opinion | Number of teenagers |
|---------|-------------------|
| Necessary | 20 |
| Waste of time | 15 |
| Sometimes useful | 10 |
| No opinion | 5 |
A)All teenagers think homework is necessary.
B)More teenagers think homework is necessary than those who think it is a waste of time.
C)Most teenagers have no opinion about homework.
D)The number of teenagers who think homework is a waste of time is higher than those who think it is necessary.