Combine the phrases and rewrite the sentence using the active voice.
Robots are built by engineers, the process is complex.
Engineers build robots using a complex process.
Complete the following task based on the instruction and optional input provided.### Instruction:
Combine the phrases and rewrite the sentence using the active voice.

### Input:
Robots are built by engineers, the process is complex.

### Output:
Engineers build robots using a complex process.