Since ～んです attaches to the plain form (dictionary form, nai -form, ta -form, etc.), you must be confident in your verb conjugations before attempting these exercises.
For a complete walkthrough of all Renshuu B answers with detailed verbal explanations, you can follow these step-by-step video tutorials: Lesson 26－Minna no Nihongo RenshuB Answers Sora - そら Lesson 26－Minna no Nihongo RenshuB Answers Sora - そら Minna No Nihongo Lesson 26 Renshuu B Answers
Here is the complete answer key for Minna no Nihongo I (Lesson 26) , along with the original question prompts and explanatory notes for each item. Since ～んです attaches to the plain form (dictionary