Frank Water was a strong man. He could not lift the rock. The rock weighed over four hundred pounds. (compound — complex sentence)
Frank Water was a strong man, but he could not lift the rock, which weighed over four hundred pounds,
Frank Water was a strong man. He could not lift the rock. The rock weighed over four hundred pounds. (compound — complex sentence)
Frank Water was a strong man, but he could not lift the rock, which weighed over four hundred pounds,