The SI base units are:
Base Quantity - - - - Unit - - - - Symbol
length - - - - - - -metre or meter - - m
mass - - - - - - - - - - kilogram - - - kg
time - - - - - - - - - - second - - - - - s
electric current - - - - ampere - - - - A
temperature - - - - - - kelvin - - - - - K
amount of substance - - mole - - - - mol
luminous intensity - - - candela - - - - cd
Note: abbreviations must have a particular case eg K is the symbol for kelvin but k is the symbol for kilo.
Three base units? There are three dimensions when an object is located in space? Width, breadth and height but in science all three of these are considered to be a length.