50. According to the passage, which of the following statements about the brain MRI scans is true? (A) In order to find the nature of brain fog, a team of British researchers conducted a survey in the Northern area of UK. (B) Researchers analyzed MRI scans from the UK Biobank study, which had only started to scan volunteers’ brains since 2020. (C) Researchers found that mild infections display no identifiable change to the brain. (D) Researchers found that obvious changes may be identified in areas that are crucial for encoding and retrieving memories, and executive function.