To find out how many eyeglasses the doctor will prescribe in a month with 24 work days, you need to multiply the number of patients per day by the number of work days in the month.
If the doctor prescribes eyeglasses for about 6 patients a day, the calculation will be:
\[ 6 \text{ patients/day} \times 24 \text{ days} = 144 \text{ patients} \]
Thus, the doctor will prescribe eyeglasses for 144 patients in a month.
So, the answer is A 144.