The correct answer is option 3, which states that the main absorbing organs of plants are the root and leaf. Let`s dissect each option to understand why this is the correct answer.

Option 1 states that only the root is the main absorbing organ of plants. While roots do play a crucial role in absorbing water and minerals from the soil, they are not the only organ responsible for absorption. Plants also absorb water and nutrients through other parts, so this option is not completely accurate.

Option 2 states that only the leaf is the main absorbing organ of plants. While leaves do have stomata, which allow for gas exchange and some absorption, they are primarily responsible for photosynthesis and respiration. Absorption of water and minerals is not their main function, so this option is also not completely accurate.

Option 4 states that not only the root and leaf but also the bark is the main absorbing organ of plants. However, the bark is primarily responsible for protecting the plant and transporting nutrients, rather than absorption. Therefore, this option is not correct either.

In conclusion, option 3 provides the most accurate answer by stating that the main absorbing organs of plants are the root and leaf.