The correct answer is option B, that is, fewer births.
Aging of Europe also called greying of Europe, refers to a demographic process in Europe featured by a reduction in fertility, higher life expectancy, and a decrease in mortality rate among the European populations. Higher life expectancy and low birth rates donate to the modification of Europe's population pyramid shape.
The most substantial modification is the transformation towards a much older population composition, leading to a reduction in the ratio of the working age, while the number of the retired population enhances.