The correct answer is A. The sample is not a heterogeneous mixture
Explanation:
A heterogeneous mixture includes two or more materials and these are not completely integrated. Due to this, in most cases, if a heterogeneous mixture is filtered it is possible to separate its parts. This did not occur when Ben filtered the substance, which shows it is likely the substance is not a heterogeneous mixture. Moreover, a heterogeneous mixture does not show uniformity in terms of appearance or properties, which shows this definitely not heterogenous and Ben can safely conclude this.
