Classify concurrency anomaly between two transactions

Two transactions T1 and T2 run concurrently and access the same data item A. Their operations (in order of time) are:

1. T1 reads A = 100 .
2. T2 reads A = 100 .
3. T1 writes A = A + 10 (so conceptually writes 110 ).
4. T2 writes A = A - 10 (using its previously read value 100 , so writes 90 ).

Which description best characterizes the concurrency problem here?

Options:

• A. This operation cannot be repeatably read (non-repeatable read).
• B. This operation has no problems.
• C. This operation reads dirty data.
• D. This operation loses modifications (lost update).