In "where have you gone, charming billy? " why can't paul stop laughing at the thought of billy boy dying?
a). he feels that death in general is funnier than it's tragic.
b). he finds it ironic that billy boy died of a heart attack in a war.
c). he believes that billy boy deserved to die a more heroic death.
d). he knows that billyboy would've found it amusing to die that way.