Wind speeds increase higher up from the earth's surface because

a. friction from landscape features doesn't slow them down.
b. oxygen levels are decreased, making air movement quicker.
c. the atmosphere is composed of heavier molecules at lower atmospheric levels.
d. the wind is augmented by the solar wind.

The difference of sample means of two populations is 55.4, and the standard deviation of the difference of sample means is 28.1. which statement is true if we are testing the null hypothesis at the 95% confidence level? a. the difference of the two means is significant, so the null hypothesis must be rejected. b. the difference of the two means is significant, so the null hypothesis must be accepted. c. the difference of the two means is not significant, so the null hypothesis must be rejected. d. the difference of the two means is not significant, so the null hypothesis must be accepted.