What semimetal can form four single covalent bonds.

The right answer is Sillicon.

Silicon (Si) is the chemical element of atomic number 14. It is the most abundant element in the earth's crust after oxygen, or 25.7% of its mass, but it is comparatively only present in relatively small quantities in the material constituting the living.

It is a semi-metal, ie it does not meet all the criteria to be defined as being a metal.

It has four free electrons in the last orbit, so it is able to form four covalent bonds. (the carbon can form 4 covalent bonds but it is not a semi-metal)