Final answer:
The yellow sign indicating merging traffic ahead is a warning for drivers to prepare for lanes combining, which corresponds to option B. Merging traffic ahead.
Step-by-step explanation:
A yellow sign indicating merging traffic ahead is a common road sign used to alert drivers that two traffic lanes will be combining into one. The correct interpretation of this sign is 'B. Merging traffic ahead'. This sign serves as a warning so that drivers can prepare to allow traffic to merge from another lane, ensuring both safety and the smooth flow of traffic. It's important to stay alert and possibly adjust speed or change lanes if necessary when you see this yellow warning sign.