The correct option is C isthmus
Females have two fallopian tubes that extend laterally from the uterus. Each fallopian tube consists of three regions: infundibulum, ampulla and isthmus.
The isthmus of the fallopian tube is a narrow, thick walled portion that joins the uterus.
The lower cylindrical portion of the uterus which opens into the vagina is known as the cervix.
The funnel shaped portion of each fallopian tube which is close to the ovary is called infundibulum.
Ampulla is the widest and the longest part of the fallopian tube.
Hence the part of the fallopian tube closest to the uterus is isthmus.