I Need Help with all these questions please.

A team of researchers (Singer, et al., 2000) used the Survey of Consumer Attitudes to investigate whether incentives would improve the response rates on telephone surveys. A national sample of 735 U.S. households was randomly selected, and all 735 of the households were sent an "advance letter" explaining that the household would be contacted shortly for a telephone survey. However, 368 households were randomly assigned to receive a monetary incentive along with the advance letter, and the other 367 households were assigned to receive only the advance letter.

(a) Identify the observational units in this study.

(b) Identify the explanatory variable.

(c) Identify the response variable.

(d) Describe in words the parameter of interest in this study.

(e) State the null and alternative hypotheses for testing whether incentives improve the response rates on telephone surveys.

(f) If these researchers find a statistically significant difference in the response rate between these two groups, would you be willing to draw a cause-and-effect conclusion? Justify.