Identify the labeled parts of the flower.

• F points to the anther, which is part of the stamen (male reproductive organ).
• G points to the petals, which are often brightly colored to attract pollinators.
• H points to the sepals, which are the leaf-like structures at the base of the flower that enclose the bud.

The sepals (labeled H) are responsible for enclosing and protecting the delicate inner parts of the flower when it is still a bud.

Based on the identification, H is the part that protects the flower during the bud stage.

The correct option is B.
$\boxed{\text{B. H}}$