en bogus. But the announcement made this week by Woo Suk Hwang, of Seoul National University in South Korea, and his colleagues, is serious. It is the first to achieve the accolade of publication in a peer-reviewed scientific journal. Dr. Hwang's work appears in Science.

The terminology of human development has become slippery over the past few years, in the hands of both "life-begins-at-conception" propagandists who want to stop this sort of research, and publicity-seeking scientists who have claimed more than they have really achieved．What Dr. Hwang and his team have created is not what developmental biologists would normally refer to as an embryo. But it is a genuine scientific advance. South Korea's researchers have taken egg cells from volunteer women, removed the nuclei from those cells (which contain only half of the genetic complement required to make a human being, since the other half is provided by the sperm), and replaced each nucleus with one taken from one of the volunteer's body ceils (which contains a full genetic complement). Given a suitable chemical kick-start, such re-nucleated cells will begin dividing as though they were eggs that had been fertilised in the more traditional manner. Since they have all of the mother's genes, they count as clones.

Then the team cultured the dividing eggs until they had formed structures called blastocysts, with a few dozen cells each. This is the significant advance. At this stage the structure, though still just a featureless ball of cells, has started to differentiate into the body's three basic cell types (known as endoderm, mesoderm and ectoderm). The researchers were able to extract cells from some of their blastocysts, and grow tissues containing all three cell types.

These are so-called stem cells, which can be directed to form. a wide variety of the specialised cells from which organs are built. That, not the creation of new human beings, is the stated reason for this sort of research, since specialised ceils made this way might be used to replace the cells lost in diseases such as Parkinson's and type-I diabetes. This process is known as therapeutic cloning.

No doubt Dr Hwang's scientific success will sharpen the debate between those who see therapeutic cloning as a potential force for good, and those who see it as a step on the road to a cloned human being. The former have been queuing up to praise the scientist's work. It is "a major med- ical milestone" that could help spur a "revolution", said Robert Lanza, a cloning expert.

But opponents of therapeutic cloning should not worry too much yet. The road from a blast cyst to a baby is a long and complex one. Nevertheless, the South Korean breakthrough makes it more urgent than ever that legislation be passed differentiating clearly between therapeutic and reproductive cloning—permitting the former and prohibiting the latter.

What does the word "bogus" (Line 2) most probably mean？

A．Different.

B．Fake.

C．Bold．

D．Genuine.