A sentence contains a mistake. Identify the mistake.
She has been studying hard since yesterday afternoon.
The input sentence appears to be grammatically correct and there is no mistake to identify.
Complete the following task based on the instruction and optional input provided.### Instruction:
A sentence contains a mistake. Identify the mistake.

### Input:
She has been studying hard since yesterday afternoon.

### Output:
The input sentence appears to be grammatically correct and there is no mistake to identify.