Let A be the set of all strings of 0's, 1's, and 2's that have length 4 and for which the sum of the characters in the string is less than or equal to 2. Define a relation R on A as follows. For every s, t ∈ A, s R t ⇔ the sum of the characters of s equals the sum of the characters of t. Which of the following is true for R? (Select all that apply.) R is reflexive. R is symmetric. R is transitive. R is neither reflexive, symmetric, nor transitive.