Which of the following statements is true of the skip questions used in a questionnaire?

Question $3$ options:

They are used to screen the respondents of surveys.

They are difficult to use in online surveys.

They appear at the beginning of the questionnaire to encourage respondents to complete the questionnaire.

They are difficult to code because of their closed$-$ended nature.

They help ensure that only specifically qualified respondents answer certain items in the questionnaire.