From the words or group of words lettered A to D, choose the word or group of words that best completes each of the following sentences. Scarcely had I open...

Answer Details

The correct option to complete the sentence is "when". This is because "when" is used to refer to a point in time after which something else happens. In this case, the sentence suggests that the person had just opened the door and immediately the dog came running in, indicating that the two events happened in quick succession. Therefore, "when" is the most appropriate word to use in this context.