Choose the polynomial that is described. A trinomial in one variable of degree 3 Select one: a. $4 r^{2}-9 t+7$ b. $3 r^{2}+4 t-9$ c. $4 r^{3}$ d. $4 r^{3}-9 t+7$

Step 1 ：A trinomial is a polynomial with three terms. We are looking for a trinomial in one variable of degree 3. The degree of a polynomial is the highest power of its variable.

Step 2 ：Option a. \(4 r^{2}-9 t+7\) is a trinomial, but its degree is 2, not 3.

Step 3 ：Option b. \(3 r^{2}+4 t-9\) is also a trinomial, but its degree is 2, not 3.

Step 4 ：Option c. \(4 r^{3}\) is a monomial of degree 3, not a trinomial.

Step 5 ：Option d. \(4 r^{3}-9 t+7\) is a trinomial and its degree is 3, which meets all the requirements.

Step 6 ：So, the correct answer is d. \(4 r^{3}-9 t+7\)

Step 7 ：\(\boxed{4 r^{3}-9 t+7}\) is the final answer.