Inferential tests

I have been struggling with these questions for days now (see file attached). Can you please help? thanks.

See attachment for full set of questions:

30. A retailer wants to obtain some current data on his customers' demographics (age, income, household size) and product preferences. He surveys all customers in his store that day. This sampling design is called:
a. simple random sampling
b. stratified random sampling
c. convenience sampling
d. purposive sampling

31. Explain what problems (if any) the retailer may encounter with this sampling strategy.

Use the scenario below to answer questions 32 and 33.

In California's San Joaquin valley, intensive irrigation has washed selenium from the soil into the drainage channels and rivers emptying into the San Francisco Bay (selenium is toxic to animals in high concentrations). Selenium concentrations were randomly sampled in two drainage channels: channel A drains fields with intensive irrigation; channel B drains fields with moderate irrigation. Each sample contains 15 observations (samples have normal distributions). Researchers want to test if selenium concentrations are higher in channel A.

32. The hypotheses for this test are:

a. Non-directional : A = B
: A B

b. Directional : A B
: A > B

c. Directional : A B
: A > B

d. Directional : A B
: A < B

e. Non-directional : A = B
: A B

33. To reject the null hypothesis at a 99% confidence level, the test statistic must be greater than the critical t value of

a. 2.47
b. 2.76
c. 2.05
d. 1.70
e. 2.46

Use the scenario below to answer questions 34 and 35.

A researcher is studying salinity levels during spring runoff in 5 estuaries along the BC coast. Samples were taken in random selected locations within each estuary. Salinity data are assumed to be normally distributed.

34. In reviewing the data, the researcher has doubts about the reliability and accuracy of the instrument used to measure salinity. Which test can the researcher use to answer the research question?

35. The researcher wants to focus specifically on two estuaries for a portion of the study. Which test can he use to determine if significant differences exist between the two selected estuaries?

Thanks a lot for this help.