Calcium is the element that is present in both cement and bones. In cement, calcium is a key component of calcium silicate compounds, which contribute to the strength and durability of the material. In bones, calcium is a vital mineral that provides structural support and strength. It plays a crucial role in various physiological processes in the human body, including muscle function and nerve signaling.

An Admiral of the fleet is a military naval officer of the highest rank. In many nations, the rank is reserved for wartime of ceremonial appointments. It is usually a rank above admiral (which is now usually the highest rank in peace-time for officers in active service) and is often held by the most senior admiral of an entire naval sevice.

Methane is the gas that can cause explosions in coal mines. Methane is a highly flammable gas, and when it accumulates in high concentrations in confined spaces like coal mines, it poses a significant risk. Methane explosions can occur if the gas comes into contact with an ignition source, such as a spark or flame, leading to a dangerous explosion. That's why proper ventilation and safety measures are crucial in coal mines to prevent methane buildup and potential explosions.