The melon the Smiths served at dinner would have tasted___if it had been put in the fridge for a little while.

It is obvious that water is to be _____to the development of life.

I put the medicine on the top of the desk to make sure it would not be _____ to my son.

 As the party was very informal, Jack stood there looking stiff and     in his formal dress. 

．People like taking photos because photos are the _______ of youth and history and can remind us of many happy scenes.