During her current pregnancy, loraine has been extra careful to avoid foods that could potentially cause foodborne illness. even though she loves greek salad, at lunch today she had to order something else because the waiter could not confirm whether or not the feta cheese on the salad was pasteurized. why should pregnant women avoid unpasteurized cheese?
a) unpasteurized cheese can contain prions that can cross the placental barrier and cause foot-and-mouth disease and spontaneous abortion or stillbirth. b) unpasteurized cheese can contain botulism spores that can cross the placental barrier and can cause botulism and spontaneous abortion or stillbirth. c) unpasteurized cheese can contain salmonella bacteria that can cross the placental barrier and cause salmonella and spontaneous abortion or stillbirth. d) unpasteurized cheese can contain listeria, a bacterium that can cross the placental barrier and cause listeriosis and spontaneous abortion or stillbirth.

Mantle convection  is the slow  creepingmotion of earth's solid silicate  mantle  caused by  convection  currents carrying  heat from the interior  to the planet's surface.[1][2]  the earth's surface  lithosphere, which rides atop the  asthenosphere  (the two components of the  upper mantle), is divided into a number of  plates  that are continuously being created and consumed at their opposite  plate boundaries. accretion occurs as mantle is added to the growing edges of a plate, associated with  seafloor spreading. this hot added material cools down by  conduction  and  convection  of heat. at the consumption edges of the plate, the material has thermally contracted to become dense, and it sinks under its own weight in the process of  subduction  usually at an  ocean trench.[3]this subducted material sinks through the earth's interior. some subducted material appears to reach the lower mantle,[4]  while in other regions, this material is impeded from sinking further, possibly due to a phase transition from  spinel  to  silicate perovskiteand  magnesiowustite, an  endothermic reaction.[5]the subducted oceanic crust triggers  volcanism, although the basic mechanisms are varied. volcanism may occur due to processes that add buoyancy to partially melted mantle causing an upward flow due to a decrease in density of the partial melt.secondary forms of convection that may result in surface volcanism are postulated to occur as a consequence of intraplate extension[6]  and  mantle plumes.[7]it is because the mantle can convect that the  tectonic plates  are able to move around the earth's surface.[8]mantle convection seems to have been much more active during the  hadean  period, resulting in gravitational sorting of heavier molten  iron, and  nickel  elements and  sulphides  in the core, and lighter  silicate minerals  in the  mantle.