For each statement, express the null hypothesis $H_0$ and alternative hypothesis $H_1$ in symbolic form.

1. $\ $ Fewer than one-half of all Internet users make on-line purchases.

A. $H_0: \mu \ge 0.5,$ $H_1: \mu < 0.5$
B. $H_0: p \ge 0.5,$ $H_1: p < 0.5$
C. $H_0: \mu \le 0.5,$ $H_1: \mu > 0.5$
D. $H_0: p \le 0.5,$ $H_1: p > 0.5$

2. $\ $ The mean salary of statistics professors is at least 70,000 dollars.

A. $H_0: \mu \ge 70,000,$ $H_1: \mu < 70,000$
B. $H_0: \mu > 70,000,$ $H_1: \mu \le 70,000$
C. $H_0: \mu \le 70,000,$ $H_1: \mu > 70,000$
D. $H_0: \mu < 70,000,$ $H_1: \mu \ge 70,000$

3. $\ $ IQ scores of statistics students have a standard deviation more than 15.

A. $H_0: \mu < 15,$ $H_1: \mu \ge 15$
B. $H_0: \sigma \ge 15,$ $H_1: \sigma < 15$
C. $H_0: \mu \le 15,$ $H_1: \mu > 15$
D. $H_0: \sigma \le 15,$ $H_1: \sigma > 15$