Question

1. the \yellow demarcation bar\ marking indicates

○a. runway with a displaced threshold that precedes the runway.
○b. a hold line from a taxiway to a runway.
○c. the beginning of available runway for landing on the approach side.

Explanation:

The "yellow demarcation bar" is a marking on a runway. A displaced threshold means part of the runway (the beginning part for landing in some cases) is not available for landing. The yellow demarcation bar is used to indicate a runway with a displaced threshold that precedes the runway. A hold line from a taxiway to a runway is a different marking (usually a hold - short line). The beginning of available runway for landing on the approach side is indicated by the runway threshold itself (not the yellow demarcation bar).

Answer:

A. runway with a displaced threshold that precedes the runway.