Specialization causes individuals and nations to rely on one another thus increasing the degree of

They increasing the degree of production efficiency.
Due to specialization, one nation could produce a certain product with lower cost or greater quality compared to other nations.
Because of this, other nations could simply fulfill the need for that specific product from that specialized nation, and choose to allocate their time and resources to produce another type of products.

It is false that during exercise, the oxygen concentration in the blood increases to twice that of resting levels. As a matter of fact, the oxygen either stays the same or decreases, or it may increase slightly than it used to be when the person was resting, but it definitely does not double while exercising. Hope this helps. Let me know if you need additional help!