Select the most appropriate option to fill in the blank.
We saw some children ______ with one another as we were walking around.

Correct option is D

The correct option to fill in the blank in the sentence "We saw some children ______ with one another as we were walking around." is option (d) quarrelling.
· The sentence structure indicates a continuous action observed in the past, which is best expressed using the present participle form of the verb. In this case, " quarrelling" fits perfectly as it describes an ongoing action that was happening concurrently with the action of walking around.
Why Other Options Are Incorrect:
· (a) quarrels: This is the plural form of the noun "quarrel," not a verb form, and does not fit grammatically in this sentence.
· (b) to quarrel: This infinitive form suggests intention rather than an ongoing action, which doesn't suit the context of something that was already happening as observed.
· (c) quarrelled: This is the past simple tense form of "quarrel," which would suggest the action was completed in the past, not ongoing as indicated by the sentence context.