A demonstrative adjective shows where the thing it modifies is in space or time. The four demonstratives are paired in relation to distance: this and these
suggest here or a close position or time; that and those suggest there or a remote position or time. They are also paired in relation to number: this and that are singular forms; these and those are plural forms.
This car is the one we bought. That car would have been impractical. These car salesmen are a unique breed. Those men are not to be trusted.
When you use a demonstrative adjective to modify a grouping noun like class, kind, sort, type, and variety, match the number of the adjective and the noun. Use a singular adjective with a singular noun and a plural adjective with a plural noun.
this class these classes
this kind these kinds
this variety these varieties
The object of the preposition of("this kind of," "these kinds of") should also agree in number with the demonstrative adjective and its noun.
This kind of pears is best.
These hinds of pear(s) are best.
