The correct option is A flexible
Option B is correct, as it's mentioned in the line "A spirit of bamboo. Bend with the wind and thus survive". 'Bend and thus survive' refers to flexibility. The poets wishes for her friend for the spirit of bamboo, due to its flexibility and ability to come back after the storm.
Options A, C and D are incorrect as these qualities (bad, mischievous, tall) are neither mentioned nor implied in the poem.