Answer:
The correct answer is letter "B": While manufacturing has led to...
Step-by-step explanation:
Transition phrases are "parts of speech" used to help the reader understand how and idea is connected to other within the same text. They also, introduce a new idea of the same topic that is being discussed.
In the example, by saying "While manufacturing has led to..." the author explicitly lets the reader know that a new idea is going to be discussed on the same matter.