答案：A

解析：

Choice A is correct. Find the cost per kilowatt-hour for each of the three plans.

For Plan A:
$106.50/930kWh≈$0.11per kWh
For Plan B:
$110.70/900kWh≈$0.12per kWh
For Plan C:
$115.20/810kWh≈$0.14per kWh

Plan A has the lowest cost per kilowatt-hour.