WAEC - English Language (2004 - No. 9)

In each of the following sentences, there is one word underlined and one gap. From the list of words lettered A - D, choose the word that is most nearly opposite in meaning to the underlined word and that will, at the same time, correctly fill the gap in the sentences.
It is curious how Bayo can be so carefree in his ways while his younger brother is so..........,,