Cells in `G_(0)` state remain _____ but no longer proliferate unless
called on to do so

Answer

### Step-by-Step Solution:

1. **Understanding the G0 Phase**: The G0 phase, also known as the quiescent phase, is a stage in the cell cycle where cells exit the active cycle of division. It is important to recognize that cells in this phase are not dead; rather, they are in a state of dormancy.

2. **Characteristics of G0 Phase**: Cells in the G0 phase remain metabolically active. This means they continue to carry out necessary cellular functions, such as maintaining their structure, producing proteins, and responding to environmental signals, but they do not undergo division.

3. **Proliferation in G0 Phase**: The question states that cells in the G0 state do not proliferate unless called upon to do so. This implies that under certain conditions (like injury or growth signals), these cells can re-enter the cell cycle and begin to divide again.

4. **Final Answer**: Therefore, the correct completion of the statement is: "Cells in G0 state remain **metabolically active** but no longer proliferate unless called on to do so."