The school has a signal shielding for exam help.

If your mobile phone shows a 2G network, you can make phone calls and send text messages. I just can't get on the Internet, because the 2G network speed is too slow. It is estimated that the 2G signal in your school is too strong and the shielding power is too small to be shielded. Normal cell phone signal shielding will shield all signals of 2G 3G 4G. In this case, it is no good to call and send text messages.