Read the paragraph.

my friend mario seems to fall in love at the drop of a hat. if a girl smiles at him, talks to him, or even glances his way, he takes it as a sign that they are meant to be together!

what are the meanings of the highlighted idiom at the drop of a hat as it is used in the paragraph?

(select all that apply.)

in an instant
without explanation
with tremendous effort
for the worse