Answer:
Option). duplication.
Step-by-step explanation:
Mutations are permanent changes in DNA, due to change in its nucleotide sequence. A mutation that occurs due to replication or duplication of a portion of genetic material is known as duplication.
As altered sequence in given bacterium represents duplication of three guanine nucleotides, the type of mutation that caused this sequence change is duplication.
Original sequence: actgggatcct
Altered sequence: atcggggggatcct
Thus, the correct answer is 'duplication.'