B

Crude Birth Rate (CBR) = (No. of live births ÷ Mid-year population) × 1000.  
A rural sub-centre is normed to cover ≈5000 people in plain areas [Sachdev, 2000, PMID 10657285].  
If CBR = 20/1000, expected births (and therefore pregnancies to be registered) = 20 × 5000 / 1000 = 100 [Martin, 2008, PMID 18381544].