Which one of the following is not a true fruit?

A. Apple
B. Grapes
C. dates
D. plum

Apple is not a true fruit. A fruit is said to be false when it develops from the ovary along with adjoining accessory from the ovary along with adjoining accessory floral parts like sepals, petals, thalamus etc. Example, apple, fig etc.
A true fruit is that fruit that develops from ovary part of the flower. Example, mango, maize etc.