**Core Concept**
The ureter's entry into the bladder is a critical anatomical feature that facilitates the proper functioning of the urinary system. The ureteral orifice is a specific location where the ureter opens into the bladder, and its position is determined by the surrounding anatomical structures, particularly the trigone.

**Why the Correct Answer is Right**
The ureter enters the bladder at the lateral angle of the trigone, which is a triangular area formed by the two ureteric orifices and the internal urethral orifice. This location allows for efficient emptying of urine from the bladder and prevents backflow of urine into the ureters. The trigone serves as a critical anatomical landmark, and its relationship with the ureteral orifices is essential for understanding normal urinary tract anatomy and identifying potential abnormalities.

**Why Each Wrong Option is Incorrect**
**Option A:** The ureter does not enter the bladder at the medial angle of the trigone, which would be an atypical location and could potentially lead to urinary tract obstruction.
**Option C:** The ureter does not make an angle when entering the bladder; instead, it opens into the bladder at a specific location.
**Option D:** The ureteral orifice is not straight; it is a distinct opening that allows for the efficient emptying of urine from the bladder.
**Option E:** The ureteral orifice is not valveless; it is a functional orifice that allows for the free flow of urine from the ureter into the bladder.

**Clinical Pearl / High-Yield Fact**
The trigone is a critical anatomical landmark in the bladder, and its relationship with the ureteral orifices is essential for understanding normal urinary tract anatomy. The trigone is formed by the two ureteric orifices and the internal urethral orifice, and its presence helps to facilitate the proper functioning of the urinary system.

**Correct Answer: 2. At lateral angle of trigone**