Teacher:In this task, you will be given sentences in which your task is to recognize the name of the organ of the body. An organ is a collection of tissues that structurally form a functional unit specialized to perform a particular function. Although there might be several correct answers, you need to write one of them.
Teacher: Now, understand the problem? Solve this instance:  Tumor markers such as alpha - fetoprotein , human growth hormone , carcinoembryonic antigen , and placental alkaline phosphatase were negative .
Student:
placental