____ for London on business upon myarrival, so I didn’t see him.

They ______ on the program for almost one week before I joined them, and now we _____on it as no good results have come out so far

My classmate Mingming is_________than me, but I am_____________than him.

The sign means “ _____.”

Many environmentalists think that carbon dioxide is _______ for the global warming, which affects billions and billions of species across the globe.[ ]