The correct option is A protonema
In the life cycle of mosses, the gametophyte consists of two stages,
1. The first stage develops directly from the spore and is known as the protonema stage. It is a creeping, green, branched and frequently filamentous stage.
2. The second stage is the leafy stage. It develops from the secondary protonema as a lateral bud. It consists of upright, slender axes bearing spirally arranged leaves.
Frond is the leaf or leaflike part of a palm, fern, or similar plant.
The axoneme is the skeleton or the innermost structure of a cilia or flagellum.