Update part7a.md

Grammar error

Author: leburgeon

src/content/7/en/part7a.md

@@ -9,7 +9,7 @@ lang: en
 
 The exercises in this seventh part of the course differ a bit from the ones before. In this and the next chapter, as usual, there are [exercises related to the theory of the chapter](/en/part7/react_router#exercises-7-1-7-3).
 
-In addition to the exercises in this and the next chapter, there are a series of exercises in which we'll be revising what we've learned during the whole course, by expanding the BlogList application, in which we worked on during parts 4 and 5.
+In addition to the exercises in this and the next chapter, there are a series of exercises in which we'll be revising what we've learned during the whole course, by expanding the BlogList application, which we worked on during parts 4 and 5.
 
 ### Application navigation structure