Offer is higher than Predicted Grades?

I received a conditional offer from Newcastle university, which I'm very pleased about. Although, I'm very confused about their offer.

Firstly, my predicted grade is A (Psychology), B(Biology) and B (English Lit) --->AS grades = B (Psychology), C (English Lit), D (Biology), and E(Chemistry) -I dropped chemistry.

Their standard offer was ABB for Molecular and Cellular Biology, so I understand why they'd offer me ABB. BUT they specified that they want an 'A' in Biology and 'B's in my other two subject.

Is there a reason for this? It'll probably motivate me to revise hard and work for that 'A' but from getting a 'D' in AS?!?! I did say in UCAS I'm re-sitting Biology Unit 2, which I got a 'D' at (My ISA= C and Unit 1 =C) I just don't understand why they'd make an 'specific' offer seeing as though I achieved a 'D' at AS Like, i'm sure they know that there's a 'HIGH CHANCE' of me not getting that 'A'??? so there's a high chance of me not meeting their offer??? meaning I'll probably just not get into the uni at results day?

Can someone please clarify this for me

This is normal, unis do specify which subject they want a grade in
However if you miss your offer by one grade or a couple of UMS they still may also take you
Also I repeated the yr
My bio first yr was a U
Second yr got a C
Hoping to retake the bad modules and get an A