How many arrangements of four 0's (zeroes), two 1's and two 2's are there in which the first 1 occur before the first 2?

How many arrangements of four 0's (zeroes), two 1's and two 2's are

1.	How many arrangements of four 0's (zeroes), two 1's and two 2's are there in which the first 1 occur before the first 2?
A.	420
B.	360
C.	320
D.	210
Answer» E.