1, The test was very difficult. We couldn't have good marks.
--> The test was too difficult for us to have good marks.
--> The test was not easy enough for us to have good marks.
2, Her mother was very sick. She couldn't go to work yesterday.
--> Her mother was too sick for her to go to work yesterday.
--> Her mother was not strong enough for her to go to work yesterday.
3, He ran very quickly. I didn't catch him.
--> He run too quickly for me to catch him.
--> He didn't run slowly enough for me to catch him.
4, The fruit is very high. I can't get it.
--> The fruit is too high for me to get it.
--> The fruit is not low enough for me to get it.