$4$ of $15$

The instruction code: add $t$1,$ $t$2,$ $t$3$ does which of the following?

computes the sum of $$t2$ and $$t3,$ then adds it to the value of $$t1$ computes the sum of $$t1$ and $$t2,$ then writes the sum into $$t3$ computes the sum of $$11,$$$t2,$ and $$t3$ computes the sum of $$t2$ and $$t3,$ then writes the sum into $$t1$