The primary net productivity of an ecosystem refers to the rate at which new tissues are formed by producers, such as plants, through photosynthesis. These producers convert solar energy into chemical energy, which is stored in their tissues. However, not all of this energy is available for consumption by other organisms in the ecosystem.

The amount of net primary productivity that is eaten and digested by herbivores is a significant aspect of energy flow in an ecosystem. It determines the amount of energy available to support the growth and reproduction of herbivores, as well as the subsequent transfer of energy to higher trophic levels.

The correct answer to the question is option B: 10%. This means that approximately 10% of the net primary productivity of a terrestrial ecosystem is consumed and digested by herbivores.

Here's a detailed explanation:

1. Understanding Net Primary Productivity:
- Net primary productivity (NPP) is the difference between the energy captured by producers through photosynthesis and the energy they use for their own respiration.
- NPP represents the energy available for consumption by herbivores and transfer to higher trophic levels.

2. Energy Losses in Trophic Transfers:
- As energy flows through trophic levels, there are energy losses at each transfer.
- When herbivores consume producers, they do not digest and absorb all of the energy contained in the plant tissues.
- Some energy is lost as waste (e.g., undigested plant material), while some is used by herbivores for respiration and other metabolic processes.

3. The Efficiency of Energy Transfer:
- The efficiency of energy transfer between trophic levels is typically low.
- On average, only about 10% of the energy consumed by herbivores is converted into new biomass (growth and reproduction).
- This means that herbivores can only utilize about 10% of the energy available in the plant tissues they consume.

4. Factors Influencing Energy Transfer Efficiency:
- Several factors contribute to the low efficiency of energy transfer in ecosystems, including metabolic inefficiencies, energy losses as heat, and energy expended in movement and other activities.
- Additionally, the structure and composition of the food web, as well as environmental factors, can also influence energy transfer efficiency.

In conclusion, approximately 10% of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores. This low energy transfer efficiency between trophic levels highlights the importance of primary productivity in sustaining energy flow and supporting the functioning of ecosystems.