Hey there! Hello!
Covalent bonds are those made by ions that share electrons. The main goal that these ions have is to become neutral. For example, if you have an ion that has a charge of 1+, like hydrogen, it means that it will take one electron that another ion has and is willing to share (it has one less electron than it does protons, giving it a positive charge). If there is a, say, chlorine ion around, which has a 1– charge (meaning that it has one more electron than protons), it will share it with the hydrogen, bonding them together and making them both neutral. This covalent bond will make HCl, or Hydrogen Chloride.
Your answer is A. I wouldn't confuse this with C, since the ions are not exchanging electrons, only sharing them with each other.
Hope this helped you out! Feel free to ask me any additional questions if you have any.
