Tallest Angiosperm is

Angiosperms are the plants that bear flowers and fruits.

The word angiosperm is derived from the Greek word ‘angeion’ and ‘sperma’ meaning those plants that produce their seeds enclosed in a fruit.

Eucalyptus regnans is the tallest angiosperm and Wolffia arrhiza is the smallest angiosperm.

Hence the correct answer is B i.e., Eucalyptus