Another corrected answer on Brilliant.org.

Angles DAB and BCD are very acute as their opposing side (BD) is the smallest (2). BDC is similarly acute, opposite the shorter of sides length 6 or 5 (BC). ABC is the only obtuse angle of the choices.

from Twisty's Mind come Twisted Products

Another corrected answer on Brilliant.org.

Angles DAB and BCD are very acute as their opposing side (BD) is the smallest (2). BDC is similarly acute, opposite the shorter of sides length 6 or 5 (BC). ABC is the only obtuse angle of the choices.