Complex sentence: In the recapitulation, the bass line in the first theme rises to B-flat instead of descending to F (as in the exposition), and the second theme enters in B minor, instead of F-sharp minor.
Split into simpler sentences: In the recapitulation, the bass line in the principal subject rises to B-flat instead of descending to F (as in the exposition). The transition enters in B minor, instead of F-sharp minor.