Explanation
Correct answer: D.
Choice D is the best answer. The convention being tested is the use of verb forms within a sentence. A main clause requires a finite (tensed) verb to perform the action of the subject (in this case, "the collection"), and this choice supplies the finite present tense verb "includes" to indicate what is in the collection.
Why the other choices are wrong
Choice A
Choice A is incorrect because it results in an ungrammatical sentence. The nonfinite to-infinitive "to be including" doesn’t supply the main clause with a finite verb.
Choice B
Choice B is incorrect because it results in an ungrammatical sentence. The nonfinite participle "including" doesn’t supply the main clause with a finite verb.
Choice C
Choice C is incorrect because it results in an ungrammatical sentence. The nonfinite to-infinitive "to include" doesn’t supply the main clause with a finite verb.