BIRADS 4 - a, b or c

[lalasea]

I had ultrasound and mammograph and have been referred for a biopsy. Mass was classified as BIRADS 4 but I don't know if it's a, b, or c. Here is the report:

IMPRESSION:
LEFT BREAST: ACR CODE 4- SUSPICIOUS ABNORMALITIES. BIOPSY SHOULD BE
CONSIDERED. Ultrasound-guided biopsy is suggested.

FINDINGS:
The breast tissue is heterogeneously dense which may obscure small
masses. Today's additional views confirm the presence of a lobulated
mass measuring 8 mm in the slightly lower outer quadrant at
approximately 4-5:00, 4.5 cm from the nipple.

Ultrasound of the 3:30 location 5 cm from the nipple shows a
lobulated hypoechoic mass measuring 6 x 9 x 6 mm. The axilla is
unremarkable.

I guess I can ask the radiologist but wondering if anyone had insight.

Thank you!