To determine the most concise option that expresses the information in the underlined portion of sentence 1, we need to analyze each choice:
- NO CHANGE: This option keeps the original wording, which could be lengthy or redundant.
- Answer A: are familiar with: This option simplifies the phrasing but does not clarify what the familiarity pertains to.
- Answer B: have seen and are familiar with service: This option adds unnecessary complexity with "have seen" and is longer than needed.
- Answer C: are familiar with specially trained service: This choice effectively captures the concept of familiarity while specifying the nature of the service.
Among these, Answer C: are familiar with specially trained service is the most concise and clear representation of the original idea.
Therefore, the best answer is D: are familiar with specially trained service.