**Core Concept**
Crude Birth Rate (CBR) is a measure of the number of live births per 1,000 people in a population per year. It is a rate that takes into account the entire population, regardless of age or sex. In this context, a CBR of 20 indicates that there are 20 live births per 1,000 people per year in the subcenter population.

**Why the Correct Answer is Right**
To calculate the minimum expected number of pregnancies, we need to assume that each live birth results from a pregnancy. Assuming a gestation period of approximately 9 months, there will be approximately 12 pregnancies per 1,000 people per year, given the CBR of 20 (20 live births / 9 months = 2.22 live births per month, and 2.22 live births per month / 12 months = 0.185 live births per person per year, then 20 live births per 1000 people per year / 0.185 live births per person per year = 108.1 pregnancies per 1000 people per year, which rounds to 108 pregnancies per 1000 people per year). However, this is an approximation and does not account for miscarriages or induced abortions. Therefore, the minimum expected number of pregnancies is at least 108 per 1,000 people per year.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the gestation period and assumes that each live birth results from a pregnancy without accounting for miscarriages or induced abortions.
**Option B:** This option is incorrect because it incorrectly calculates the number of pregnancies based on the CBR.
**Option C:** This option is incorrect because it does not provide a clear calculation based on the CBR.
**Option D:** This option is incorrect because it does not account for the gestation period and assumes that each live birth results from a pregnancy without considering other factors.

**Clinical Pearl / High-Yield Fact**
When calculating the minimum expected number of pregnancies, it is essential to consider the gestation period and account for factors that may affect the number of pregnancies, such as miscarriages or induced abortions.

**Correct Answer: A. 108.**