Correct Answer: As soon as

Solution : The first option is the correct choice.

As soon as indicates that an event will happen immediately after another event. In this context, it suggests that the children ran out immediately after the bus stopped.

The meanings of other options are as follows:

• As long as implies a condition or duration.
• No sooner than suggests that one event happens immediately after another, but typically in a negative sense.
• In order that expresses purpose or intention, indicating why something is done.

Therefore, the complete sentence is: As soon as the bus stopped, the children ran out.