c. When did you first start chewing gum?

Again, the question assumes that the survey-taker chews gum at all. Second, the question gives no time frame. Do they mean the first time you ever chewed gum, the first time you chewed a certain brand of gum?

d. How much discretionary buying power do you have each year?

This question doesn't define what "discretionary buying power" is -- is the survey-taker supposed to answer in a dollar amount? It would be better to have a multiple choice question with ranges of dollar amounts to choose from. With this method, the survey designer can set the ranges in a way that is most useful for their needs.

e. Why did you decide to attend Big State University?

This open-ended question might...

The range of answers may well vary from "It was close to home," to "I liked the mascot." Once again, if the respondents were given multiple choices and then a chance to expand with an essay-style response, the data would be narrowed to what is useful but the chance to hear 'outside-the-box' answers would still exist.
f. Do you think the president is doing a good job now?

This question is vague, but it is often used to get a general idea of approval. It is useful in that limited sense, in that the answers are binary -- yes or no. If more specifics are desired -- i.e., do you agree with the president's position on Specific Bill a -- then the question needs to be redesigned.