Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: In a horrific family tragedy a 12-year-old boy is suspected to have poisoned to death his two young sisters in a Hunan province village in China. The unidentified boy told police that he gave the girls cola that he had laced with poison. The sisters, aged eight and 14, collapsed as they were walking home from school. They were bleeding from their mouths and had stopped breathing by the time they were rushed to the hospital. The sisters were reported to have died from Tetramine poisoning. The deaths come after other similar tragedies recently. Three months ago in a rural part of Shandong, China, a six-year-old boy was killed by the same toxic substance, used for rat poisoning, after eating a piece of candy he'd found outside.Unidentified boy told police he gave girls cola he had laced with poisonSisters, aged eight and 14, collapsed while walking home from schoolThey were bleeding from their mouths and had stopped breathingThe sisters were reported to have died from Tetramine poisoningIn Shandong a six-year-old boy was killed by the same toxic substanceHe died after eating a piece of candy that contained rat poison 
 Question:_ has tens of millions of rural children whose parents have left their home villages to seek work and better pay in industrial cities.

China