No one sprained any muscles there. 这句话怎么解释啊?

帮我改这道题的错
The man had fallen into the creek,and had sprained
his ankle.Although it was still August,the Canadian wilderness lay
coldly and lonely in the weak light of the afternoon sun.Every where 1_
was the dull skyline.The hills were all low-lying.There were no trees.
There was nothing besides desolation that sent fear into man’s heart.2_
“Bill!” he called again.“Bill!” There was no answer.
The man rose to his feet,shaking as if he had had a fever.He 3_
fought against the fear in his heart.He found his gun when he had 4_
dropped it in the water.
Then he continued his way slowly.The gun was now useless,for
He had no ammunition for it,but he did not leave it.
He shifted his pack to his left shoulder so as to favourite his right 5_
Ankle and hurried to the top lf a hill.From where he saw a broad val- 6_
ley,empty of life,The bottom of the valley was soft and swampy.He
pushed down,trying to follow the tracks of his companion.7_
Though he was alone,he did not lost.Farther along he kniw where 8_
to find the trail.He would follow until it came to the river,where they 9_
had left their canoe,weighting down with rocks.Under the canoe was a 10_
hiding place of ammunition for his empty gun,fishhooks and lines,and a
small net.

before he sprained his back,Morgan had spended much of his leisure time (engaged) in outdoor sports,paticularly hiking and canoeing.
这里为什么engaged是对的?不是engaging?

请将下面这句话译成中文.
Zhao Wenjing sprained her waist when doing exercise yesterday
.就这一句