Local anaesthetic injections
A fail, usually because the anaesthetic solution is out of date 
B followed by collapse is usually because of allergy to one of the constituents 
C followed by trismus after the effect of inferior dental local anaesthetic block has subsided usually indicates trauma in the region of the medial pterygoid muscle and/or a haematoma 
D except for local infiltrations should be avoided in patients with haemophilia
AB is true and CD are false AB are false and CD are true AC are true and BD are false AC are false an BD are true