• (1) ✔ Correct — “It’s been raining since morning.” → Present perfect continuous tense, correct usage.
• (2) ❌ Incorrect — “Understand” is a stative verb (expresses a state, not an action) and is not used in the continuous form. Correct form: “They understand the problem.”
• (3) ✔ Correct — “It has clear ideas.” → Proper use of “has.”
• (4) ✔ Correct — Grammatically fine.

✅ Incorrect sentence: They are understanding the problem.