C

Pattern of powers of 7 are 7 ,9,3,1 and then this pattern repeats further...

( 7^1, 7^2,7^3,7^4 and pattern repeats........)

Patters of powers of 3 are 3 ,9,7,1 and then this pattern repeats

so both 7 ^n or 3 ^n can have unit digit as 7 depending on the value of power

here we need power of 33

( pattern repeats every 4 th power ,(8*4+1) and hence we need to check the first position in power pattern where the first position is 7

this is in the power pattern of 7)

C

Wow, you're good.

brb,

pick up an mgmat number properties book, this units digit with exponents rule is in there.