Thank you for the quick response, I wonder if the two data files you provided above is the same files as the the ones on Ensembl?
"Mus_musculus.GRCm39.104.gtf.gz" and "Mus_musculus.GRCm39.dna_sm.primary_assembly.fa.gz"
I guess they are same, just different names, right? which one would you prefer to use in practice?