<span>the answer is :
permanent magnets
</span>A permanent magnet<span> is an object made from a material that is </span>magnetized<span> and creates its own persistent magnetic field. An everyday example is a </span>refrigerator magnet<span> used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called </span>ferromagnetic<span> (or </span>ferrimagnetic<span>). These include </span>iron<span>, </span>nickel<span>, </span>cobalt<span>, some alloys of </span>rare-earth metals<span>, and some naturally occurring minerals such as </span>lodestone<span>. Although ferromagnetic (and ferrimagnetic) materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field, by one of several other types of </span>magnetism<span>.</span>
Give the real pills and placebo pills to both the girls and the boys.
Males have an X and a Y chromosome thus denoting males as XY. Traits carried on chrosomes 1-22 are autosomal<span> traits. Traits carried on the X and Y chromosomes are </span>sex linked<span> traits. Not all traits on the X and Y chromosome are to do with sexual characteristics eg colour blindness is a trait found on the X chromosome.</span>