11.C:"If you are like most people,your intelligence (智力) varies from season to season."
12.B:"have a definite effect on our mental"definite一定的,限定的,就是some的意思.
13.B:concluded from other men′s work and his own among peoples in different climates that climate
14.B:Spring appears to be the best period of the year for thinking……Fall is next-best season,then winter所以夏天放假更好
15.A全文都只是阐述一个事实,所以C、D错,与place无关,B错.