Ascientist is observing a eukarotic cell and a prokaryotic cell. which structure could she only observe in the eukaryotic cell?

The correct answer would be the nucleus.

A nucleus is a membrane-bound cell organelle only found in eukaryotic cells.  

The membrane of the nucleus is termed as nuclear membrane and the gel-like content inside the nucleus is termed as nucleoplasm.

The nucleus is the controlling center of the cell as it contains DNA or genetic material of the cell.

In contrast, prokaryotic cells are primitive cells which lack membrane-bound organelles like the nucleus, mitochondria, Golgi body et cetera. The DNA of a prokaryotic cell remains suspended in the cytoplasm.

i think that you are smart and you should fit for it out

answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]