According to The Chicago manual of style,
A term ending in “(s)” is both plural and singular. If you must use such a device (and it can be a useful shorthand), you have to be prepared to adjust the surrounding context as necessary: for example, “the award(s) is (are) accounted for.” A parenthetical plural verb must correspond to the parenthetical ending. But that’s an awkward example. In general, avoid such shorthand unless it can be used simply and effectively ...
In other words, the use of this shorthand might be useful in examples such as,
- The identification number(s) of the prisoner(s) must be logged upon arrival.
- The identification number(s) of the prisoner(s) must be logged upon his (their) arrival.
However, in other cases such as the OP's, it can be ambiguous and confusing as there's no consistent way to maintain singularity or plurality thanks to the presence of the determiner, an. In such instances, it is best to reword the sentence to something along the lines of,
- Selecting one or more appropriate study topics.