They are anxious . . . . . . . . his health? A. for B. at C. about D. on

The correct answer is C. about.

The word “about” is used to express concern or worry about something. In this case, the people are concerned about the man’s health.

The other options are not as appropriate.

• The word “for” is used to express a reason or purpose. In this case, the people are not expressing a reason for their concern, they are simply expressing their concern.
• The word “at” is used to express a location or position. In this case, the people are not expressing a location or position, they are expressing their concern.
• The word “on” is used to express a topic or subject. In this case, the people are not expressing a topic or subject, they are expressing their concern.