The correct option is C fun
The line including blank (7): "It will be great ____ and I am sure we can learn a lot."
Option D: The noun 'fun' refers to any form of amusement or light-hearted pleasure. When used here, it relates to the workshop, which will be filled with enjoyment. Hence D is the correct option.
Option C: The noun 'joy' refers to 'an emotion of great delight or happiness'.
There may arise a confusion between fun and joy, but these words cannot be used synonymously: "Fun is morally indifferent and spiritually empty" whereas joy is morally as well as spiritually essential and innate. (For example, 'I felt great joy upon seeing my son receive an award.' Hence option C is incorrect.
Option A: 'Enjoy' is a verb, whereas a noun is required, since the word before the blank "great ___" is an adjective; adjectives do not modify verbs, they only modify nouns and their equivalents. Hence A is incorrect.
Option B: The word 'cheer' refers to an action, 'a shout of encouragement or praise'; it does not relate to the workshop in the passage. Hence B is incorrect.