"Then said Frigg: 'Weapons and wood will not hurt Baldr. I have received oaths from them all.'
Then the woman asked: 'Have all things sworn oaths not to harm Baldr?
Then Frigg replied: 'There grows a shoot of tree to the west of Val-hall. It is called mistletoe. It seemed young to me to demand the oath from.'
Straight away the woman disappeared."
In Norse mythology, which plant or substance did Frigg not receive an oath from to protect Baldr?
a) Weapons
b) Wood
c) Mistletoe
d) Val-hall