Which of the following is the warning sign of mental illness?

Correct option is D

All listed symptoms are recognized red flags in mental health. Significant changes in behavior, mood instability, and suicidal ideation require immediate evaluation. Explanation of options:
· (a) ✔/✘ Yes, often the first sign of mental health decline.
· (b) ✔/✘ A serious sign needing urgent mental health intervention.
· (c) ✔/✘ Could indicate disorders like bipolar or major depression.
· (d) ✔ Correct; all listed are valid warning signs.