Answer:
Jim lifted the heavy bag of concrete because he was as strong as an ox.
Explanation:
It is the fourth one because it is the only sentence describing someone/thing as strong. (as an ox.)
The first one has nothing to do with being strong.
The second one would be correct if it was "The boat was as strong as an ox as it persevered through the rough waters.", but since that isn't the sentence, it wouldn't work.
The third one is incorrect because if the toy was made to be as strong as an ox, why is it breaking into tiny pieces?
Therefore, the fourth one is right. :)
