Which of the following is not a characteristic of a tetrad?

In general in which direction does wind blow

Alaska and northern canada have a diet rich in vitamin d and their skin color is darker than predicted on the basis of iv intensity at their latitude. explain the observation:

According to the big bang theory, after the "bang," the universe remained dark until about  300,000 yearsone billion yearsthree minutesthree billion years  later, when neutral atoms began to form.