The structures that help some bacteria to attach to rocks and/or host tissues are Rhizoids, Holdfast, Fimbriae, Mesosomes.

Prokaryotic organism such as bacteria have hundreds of hair-like appendages or bristle like fibres sprouting out of cells called fimbriae, which are composed of protein and are smaller than flagella. Bacteria uses this kind of structure for attaching to cell surfaces or host tissues. This structure also helps the bacteria to adhere one another and also attach to rocks. So, the correct answer is option C.