Здравствуйте! Подскажите правильно ли я множественное число переделала на единственное? Английский знала когда-то хорошо

II. Поставьте подчеркнутые существительные в единственное число, выполнив все необходимые изменения в предложении

1. Phytodrugs are mixtures of many compounds extracted from a single or many plants.
The phytodrug is a mixture of many compounds extracted from a single or many plants.

2. Many natural plant products are used in developing pharmaceuticals.
A natural plant product is used in developing pharmaceuticals.

3. Active ingredients of plants are also frequently chemically modified.
An active ingredient of plants is also frequently chemically modified.

4. That's why in some countries, there is a clear difference between the pharmacies which are thought to sell conventional medicines and the herbalists' shops supposed to handle phytodrugs.
That's why in some countries, there is a clear difference between the pharmacy which is thought to sell conventional medicines and the herbalist's shop supposed to handle phytodrugs.

5. But these solutions differ from place to place and even from a generation to another.
But this solution differs from place to place and even from a generation to another.