How many 2 letter words can you make from FIRST?

There are 5 valid 2-letter words that can be made from the letters FIRST, and the highest scoring is if at 5 points.

5 2 letter words from first

You can make 5 words of exactly 2 letters from FIRST. The highest scoring is if at 5 points.

it: the branch of engineering that deals with the use of computers and telecommunications to retrieve and store and transmit information
si: a complete metric system of units of measurement for scientists; fundamental quantities are length (meter) and mass (kilogram) and time (second) and electric current (ampere) and temperature (kelvin) and amount of matter (mole) and luminous intensity (candela)
ti: a light strong grey lustrous corrosion-resistant metallic element used in strong lightweight alloys (as for airplane parts); the main sources are rutile and ilmenite