If presents bring less thrill now that we are grown up, perhaps
it is because we have too much already; or perhaps it is because we have
lost the fullness of the joy of giving, and with it the fullness of the
joy of receiving. Children's fears are poignant, their miseries are
acute, but they do not look too forward nor too far backward. Their joys
are clear and complete, because they have not yet learnt' always to add
'but' to every proposition. Perhaps we are too cautious, too anxious,
too sceptical. Perhaps some' of our cares would shrink if we thought
less about them and entered with more single minded enjoyment into the
happiness that come our way.

Correct Option (B)

The passage explicitly states multiple reasons for adults experiencing less thrill from presents. It suggests that this could be "because we have too much already" or "because we have lost the fullness of the joy of giving, and with it the fullness of the joy of receiving." This directly supports the statement that there can be more than one reason.

Incorrect Options:

Option (A): The passage indicates that presents bring "less thrill" to adults, not that it is "not possible" for them to feel thrilled. This implies a reduction in the intensity or frequency of the feeling, rather than its complete absence.

Option (C): The author clearly provides several potential explanations for why adults feel less thrilled by presents, such as having too much or losing the joy of giving and receiving. Therefore, the author does know why adults feel less thrilled and offers specific insights.

Option (D): The passage does not assert that adults have a diminished capacity for feeling joy or love. Instead, it suggests that adults become "too cautious, too anxious, too sceptical" and lose the "single minded enjoyment" of happiness. This points to a change in the *experience* or *approach* to joy, rather than an inherent reduction in the capacity for it.