They were to visit a park in a city but they stayed back home to listen to a program(rewrite using nominal compounds).
They want to see 'city park' in the answer (a park in a city) -- two nouns in a row, the first one (which is always singular) acting as an adjective to modify the second.

I don't see any other places in the sentences where a nominal compound can be made, but since I answered this one for you, you answer these for me:

Rewrite each with a nominal compound(s).

The children listened to a progam on the radio. (1)
Helen attended a school for learning music. (1)
The family gathered around the table in the kitchen to eat a casserole made of tuna. (2)
Matthew heard a symphony at the new hall for concerts. (1)
Some members of the forum had a good grasp of technology associated with computers. (2)

Good luck!
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Thank you mister ......Califjim....u r guidences are usefull.....