Make up negative sentences according to the model

Арина а как это решать ? пропущенные слова нужно воткнуть?

The bus isn't so fast as the train
My flat isn't so big as her flat
His voice isn't so brilliant as Caruso's
The pond isn't so deep as the river
This lecture isn't so interesting as that lecture
This hat isn't so beautiful as that hat
His article isn't so long as her article