Grapes taste sour.

Grapes are sour when they are tasted

Grapes were sour when they are tasted

Grapes will be sour when they are tasted

Grapes should be sour when they are tasted

All of the above

Active Voice: Grapes taste sour.

Passive Voice: Grapes are sour when they are tasted.

Active Voice: The surface feels smooth.

Passive Voice: The surface is smooth when it is felt.

Active Voice: Roses smell sweat.

Passive Voice: Roses are sweat when they are smelt.