Step 1: Understanding 'Diligent'.
'Diligent' refers to someone who is careful and persistent in their work or efforts. A synonym for diligent would describe the same traits.
Step 2: Analysis of options.
- Intelligent: While intelligent people may work diligently, it is not the direct synonym of 'diligent'.
- Energetic: Energetic refers to someone with vitality, not necessarily indicating diligence.
- Modest: Modesty refers to humbleness, not related to diligence.
- Industrious: Industrious means hardworking and diligent, making it the correct synonym.
Step 3: Conclusion.
The correct answer is Industrious, as it best reflects the meaning of 'diligent'.