To determine which sentences are not true based on the provided statements, we need to analyze each option:

**For Question 3:**
- A. parsley can stop bad breath.
- B. rosemary can be good for our stomach.
- C. ginger may help us warmer.
- D. coffee may help us sleep well.

If we assume that each of these statements is based on a specific passage, we need to identify which statement is factually incorrect. Generally, coffee is known to disrupt sleep rather than promote good sleep, so **D** is most likely the false statement.

**For Question 4:**
- A. There are a lot of helpful plants.
- B. There are some harmful herbs.
- C. Some flowers have poison in them.
- D. All herbs are useful.

Among these options, D is the broadest and the most likely to be false because it assumes that every herb has value, which is not true as some can be harmful or toxic. Therefore, **D** is not true.

**For Question 5:**
- A. old people want to be healthy.
- B. more and more people are interested in their health.
- C. some plants have been used in herbal medicine.
- D. herbs may not be gentler than pills.

These statements reflect general assumptions rather than specific truths from a text. However, given the increasing trend towards health and natural remedies, both A and B could commonly be seen as true. However, D implies that herbs might be as harmful as pills; since herbs are generally perceived to be gentler, **D** might be inferred as less true compared to the other statements.

In summary:
3. D is not TRUE.
4. D is not TRUE.
5. D can be inferred as less true compared to other statements.