London--- A mother has criticised "selfish" passers-by for failing to help her teenage son after he fainted   on a packed tram platform. Oliver Tiplady was on his way to school when he fainted at the tram stop. But instead of helping the 14-year-old, who was in school uniform,those nearby simply walked around him. Her mother, Susan Tiplady , said, "How can people leave a child for that matter, on the floor like that? How could they all have ignored him? They must have lacked any basic humanity and had no piry on a child." She said her son regained consciousness   about ten minutes after fainting at the tram stop last week. "He managed to get up and sit down before his friends turned up, but by then he was too embarrassed to tell them what had happened. It wasn't until he got to school that he told a teacher." she added. BEIJING - At least 15 pupils were confirmed dead after a school bus rolled over in Xuzhou, East China's Jiangsu province. The accident occurred around 6 pm on Monday .There were 29 pupils on the bus .The bus was traveling on the road when two electric bikes suddenly cut in and the driver was trying to avoid them.. The bus was produced by Shaolin Auto Co Ltd in Henan province and had a full capacity   of 52 passengers. South Korea ---South Korea's largest mobile phone operator said Thursday that it will offer cell phone users a new noise service that it says will drive away mosquitoes . SK Telecom Co. said consumers can pay 3,000 won (  ) ($2.50) to download a sound wave that can't be heard by human ears but annoys mosquitoes within a range of three feet. Customers can then play the sound just by hitting a few buttons on their mobile phones. The company claimed that the service worked during tests .The service, which begins Monday, has one drawback: it consumes as much battery power as normal cell phone rings. From the passage , we can infer   _
the accident happened because of two electric bikes . the school bus was overloaded when the accident happened . the bus driver was speeding up when the accident happened . the bus driver was driving carelessly when the accident happened.