4. If $\frac{t_{1}}{\left|t_{1}\right|}+\frac{t_{2}}{\left|t_{2}\right|}+\frac{t_{3}}{\left|t_{3}\right|}=1$, then the value of $\frac{\left|t_{1} t_{2} t_{3}\right|}{t_{1} t_{2} t_{3}}$ is ( ).
(A) -1
(B) 1
(C) $\pm 1$
(D) Uncertain
4. A.

Since $t_{1}, t_{2}, t_{3}$ are all non-zero, then $\frac{t_{1}}{\left|t_{1}\right|}, \frac{t_{2}}{\left|t_{2}\right|}, \frac{t_{3}}{\left|t_{3}\right|}$ must have two values of 1 and one value of -1. That is, $t_{1}, t_{2}, t_{3}$ have two positive numbers and one negative number.
Therefore, $t_{1} t_{2} t_{3}<0, \frac{\left|t_{1} t_{2} t_{3}\right|}{t_{1} t_{2} t_{3}}=-1$.