Epinephrine acts as a signal molecules that attaches to proteins.
1. ion-channel receptor
2. nuclear receptor
3. g-protein-linked receptor
4. receptor tyrosine kinase
5. intracellular receptor

G-protein-linked receptor

Explanation:

Epinephrine acts via G-protein-linked receptors. The heterotrimeric G proteins located within the cell are activated by G protein-coupled receptors that span the cell membrane. Signaling molecules bind to a domain on the GPCR located outside the cell, and an intracellular GPCR domain then in turn activates a particular G protein.

if your own plato the answer is b. the fern transitioned from sporophyte generation to gametophyte generation.