In the following question, choose the option that best completes the sentence. The guest would have arrived earlier but he was _______ in traffic.

The best option that completes the sentence is "held up". When we say someone is "held up", it means that they are delayed or prevented from progressing or arriving at a certain place. In this context, the guest would have arrived earlier but their progress was delayed because of traffic.
To further explain, imagine a situation where the guest was driving to their destination but encountered heavy traffic along the way. This traffic caused a delay and prevented the guest from reaching their destination on time. Therefore, the correct option is "held up".
The other options can be eliminated because they do not convey the same meaning as "held up". "Held down" means to restrain or keep someone or something in a lower position, which does not fit the context of someone being delayed in traffic. "Held about" does not have a commonly understood meaning in this context. "Held off" means to postpone or delay something, but it does not specifically refer to a person being delayed in traffic. Therefore, "held up" is the most appropriate option for completing the sentence.
It is important to analyze the word choices in the options and understand their meanings in order to determine the correct answer.