The answer is B. plant structures
hope this helps !
The word "apace" in this paragraph means "quickly" or "swiftly". The author is talking about birth rate declines, not only in the Western world, but all around the world; it is a trend that is not going to disappear or slow down anytime soon, and it is conquering the world at a pace that is becoming faster every moment. In other words, the trend is growing in speed.
It may be different for some people, some may experience abdominal pain, while others can get severe headaches, rapid weight gain.
