Questions

It is when themes of keywords are matched by AdWords to relevant content on various websites that run Google ads.

Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.

A restrictive clause is one that limits the meaning of the word it describes.

For example :: 

The girl who lives next door is beautiful.

This restrictive clause limits "the girl" to say it's specifically the one next door.

Herbivorous organisms are those that take for their food, plant parts like leaves raw in contrast to vegetarian, which means that plant products are taken raw or after being cooked.

A greenhouse gas (GHG) is any gas in the atmosphere that absorbs and emits radiation in the thermal infrared range.

The increase in average global temperatures that results from an enhanced greenhouse effect.

Effects of increased greenhouse gas emissions:

Increases in the different greenhouse gases have other effects apart from global warming including ocean acidification, smog pollution, ozone depletion as well as changes to plant growth and nutrition levels.