Rewrite the following sentence by adding one adjective.
The student was able to understand the difficult concepts.
The diligent student was able to understand the difficult concepts.
Complete the following task based on the instruction and optional input provided.### Instruction:
Rewrite the following sentence by adding one adjective.

### Input:
The student was able to understand the difficult concepts.

### Output:
The diligent student was able to understand the difficult concepts.