(1) the correct answer is c. Have a play around with this applet, you will see that by increasing the number of samples from a population, then the distribution of the sample means gets closer to normal. http://www.ruf.rice.edu/~lane/stat_sim/sampling_dist/

(2) the correct answer is d

(3) the correct answer is b. By looking at the formula for the standard error, you have a division by . Decreasing n makes smaller and thus the standard error larger, therefore increasing the width of the confidence interval.