Final answer:
During DNA replication in E. coli, a single replication bubble is formed because replication starts from a single origin and proceeds bidirectionally, thus the answer is (b) one. So the correct option is b.
Step-by-step explanation:
E. coli bacteria have a single circular chromosome that undergoes DNA replication starting from a single origin of replication. As replication begins, the double helix unwinds and is replicated in both directions, forming two replication forks that extend bi-directionally. Given this information, during DNA replication, you would expect to form a single replication bubble in E. coli because replication proceeds around the circular chromosome from that one origin of replication, creating two forks that move in opposite directions but within the same bubble.
The correct answer to the question is therefore option (b) one.