[03:57.61]Most go undetected because the explode over remote areas or the ocean.

[04:02.13]The lead scientist in the study, professor Peter Brown from western university in Montaria, Canada, says early warning systems need to be put in place.

[04:11.60]“Having some sort of system that scans the sky or continuously look for these objects just before they hit the earth,

[04:19.06]that probably is something worth doing and in case in events,

[04:21.89]a few days to a week warning would have been valuable or for no reason to be able to tell people not to look out the windows or get close to the windows when it happened.

[04:30.25]Police in Brazil are investigating reports that the Canadian pop singer Justin Bieber has been photographed painting graffiti on a wall in Rio de Janeiro.

[04:39.29]Local media said members of the teenage idols on rush told the police that Justin Bieber had been authorized by the city council to paint a wall,

[04:48.10]although not the one that appears on the photographs.

[04:50.28]Correspondents say that if found guilty of defacing a building, the singer could be sentenced to up to a year in prison.

[04:57.68]BBC news.

第三页：词汇解析

normal

难度：5星基本词汇，属常用1000词

英汉解释

adj.正常的；正规的；精神健全的