To simplify the expression \( a^{67} b^{34} \), we need to consider the format given in responses. However, since there isn't any operation in the expression provided, we can interpret it simply as it is already in its simplified form.
Based on the responses provided, the correct choice is:
a^{67} b^{34}
If you meant to perform some operations, please clarify, and I'll assist you accordingly!