Which of the following sentences contains a dependent clause?

A. Kyoto is an ancient city, but it is also a hub of modern business.

B. Until we know for certain that it's safe, no one is to go outside.

C. Acme Bottling Company is expected to go out of business soon

D. The crimson-painted gate rose forebodingly from the graveyard.

Out of the following sentences the one that contains a dependent clause is "Until we know for certain that it's safe, no one is to go outside." So, the right option is B.

Explanation:

This type of clause is formed of an arrangement of words, possesses a subject and verb, isn't able to convey a complete idea or thought and can't stand alone as a sentence. Looking at the sentence mentioned above, we see that there is no independent clause and the need of another sentence to complete the meaning of statement is needed.

"Until we know for certain that it's safe" doesn't communicate the complete meaning until "no one is to go outside," is added to it. So, that's why, the former is termed as a dependent clause.

B. Until we know for certain that it's safe, no one is to go outside.

Explanation:

A dependent clause, is a phrase containing a subject and a verb, but cannot stand on it's own as a sentence. The phrase, Until we know for certain that it's safe, cannot stand as an independent clause, (a complete sentence), once it's own, hence why it is put together with the independent clause, no one can go outside.