Practice exam q on recursion (for intro to software design)

Is this question even remotely coherent? If so help would be appreciated.

3. Write the following function. You MUST use recursion. You may use string library functions: indexing, length(), +, and substr(int n).

a. string alternate(string s): returns a string that contains every other element of s starting at the beginning. For example, alternate("dog") = "dg".

That's it. That's all the information we have for this question. Don't know how to interpret that.