Why Is a Baby Resulting from in Vitro Fertilization Refered

Why is a baby resulting from in vitro fertilization refered to as a "test tube" baby?

A) The fetus develops for awhile in an incubator in a lab.
B) Eggs and sperm are collected into test tubes prior to being reinserted into the uterus.
C) Immature eggs are collected and allowed to mature in a test tube before they are introduced back into the uterus with the sperm cells.
D) Eggs and sperm are combined in a dish in lab and after a few days, the developing embryo is transferred to the uterus.
E) No real reason since it doesn't really make sense.