What is thought to be most responsible for the salinity of the oceans

 Natural run-off from mountain ranges is thought to be most responsible for the salinity of the oceans.

After years and years of river inflow and evaporation, the salt content of the lake water built up to the present levels. The same process made the seas salty. Rivers carry dissolved salts to the ocean. Water evaporates from the oceans to fall again as rain and to feed the rivers, but the salts remain in the ocean.

*Hope this helps

Covalent bond is the correct answer