The pyramid of ................is always upright.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding the Question**: The question asks about a specific type of pyramid that is always upright. In ecology, there are three main types of pyramids: pyramid of numbers, pyramid of biomass, and pyramid of energy.

2. **Identifying the Upright Pyramid**: Among these three types, the pyramid of energy is the one that is always upright. This is because energy flows in a unidirectional manner through an ecosystem.

3. **Explaining Energy Flow**: In an ecosystem, energy is transferred from one trophic level to another. Typically, only about 10% of the energy is passed on to the next level (known as the 10% rule). For example, if the primary producers (plants) have 100 units of energy, primary consumers (herbivores) will have about 10 units, secondary consumers (carnivores) will have about 1 unit, and so on.

...