________ the earth to be flat, many feared that Columbus would fall off the edge of the earth.

The video，Gangnam Style，is becoming the first video________more than one billion views.

Mark often attempts to escape  _______  whenever he breaks traffic regulations.

Yan' an, a city        in northern Shaanxi province, has seen great progress in its tourism industry over the past few years．

Be careful when you deal with this chemical, as it will explode when ______ to sunlight.