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Explanation:
In thermoplastics, the arrangement of monomeric units is linear and in thermosetting plastics, it is cross-linked. Thermoplastics are usually soft, weak and less brittle, so can get soften on heating and stiffen on cooling. They can be melted, remoulded and recycled easily.
A keystone species helps define an entire ecosystem. Without its keystone species, the ecosystem would be dramatically different or cease to exist altogether.
The correct answer is B. Tundra
Tundras are the coldest places in the world and are located far north, around the arctic circle, and incorporates countries such as Finland, Russia, Alaska, and others.