Final answer:
The best answer for the underlined portion is 'become'.
Step-by-step explanation:
The best answer for the underlined portion of the sentence is become. The correct verb formation for this sentence is has become. The verb 'become' is used to indicate a change or transformation, and in this case, it signifies that the building changed into the Kam Wah Chung & Co Museum. 'Became' is the past tense of 'become,' but it is incorrect because the sentence is in the present perfect tense.
Learn more about Verb tense in English