Is it OK to say, 1 the effects of burning fossil fuels have reached a high degree, 2 the problems of burning fossil fuels have reached a high degree? I mean the problems are serious.

A Swedish person is a Swede. A British person is a Briton. How about "a Portuguese person" and "a Chinese person"?

A question about the other. I have three pens. One is black. Another is red. The last one is blue. Is it correct to say, "The other one is blue" instead?

recharge mental batteries? I read in an article, "A vacation gives workers a chance to recharge their mental batteries." I think recharge mental batteries refers to learning and maybe other stuff. Can you give me any other activities that may take place when one recharges his mental batteries?

"If you're buying gift cards for a large number of people, those fees can add up." I'm wondering what add up in this sentence means. I read in a dictionary To amount to an expected total. So, does it mean the sum of those fees can amount to a large sum?

Please give me some examples I'm trying to understand constructive pursuits. Can you list examples of constructive pursuits?

use of divulge Is is OK to say: He won't divulge his privacy.