The organism you described digests its food externally before absorbing it and cannot move. Based on these characteristics, the most likely answer is:
D) Fungus
Fungi are organisms that absorb nutrients from their environment after breaking down organic material through external digestion. In contrast, bacteria can also perform external digestion, but they are typically not described in the same way as multicellular fungi. Animals generally digest food internally, and protists are mostly unicellular and may not fit the description of being immobile and having an external digestion process.