Step 1: Meaning of implicit alternatives.
- An implicit alternative is a possible answer that is not stated directly but understood by the respondent.
- Making it explicit can change the response distribution.
Step 2: Analysis of given statements.
- (a) Correct — Explicit alternatives may increase selection rate.
- (b) Correct — Known as “position bias” or “recency effect” in long lists.
- (c) Correct — Split ballot method helps control order bias by rotating alternative positions.
Step 3: Conclusion.
Since all three are correct, option (d) is the right choice.
\[
\boxed{(d)}
\]