To simplify the expression \( a^{67}b^{34} \), we look for a possible common term or exponent that can be factored or simplified. However, here there are no common bases to combine or terms to reduce since \( a \) and \( b \) are different variables with different exponents.
The expression remains as:
\[ a^{67}b^{34} \]
Thus, the correct option for the expression simplified is:
a67b34