单项选择题

How much seawater has been sprayed into the Fukushima Daiichi nuclear reactors to keep them cool More (31) than the number of tons of water is the amount of sea salt that was (32) in the reactors: ninety-nine thousand pounds (33) in reactors NO. 2 and 3, and fifty seven thousand in reactor No.1, according to the Times. (34) one might suppose, it is not good for any sort of (35) to have that much salt in it. During the Berlin Airlift, one of the biggest challenges was carrying salt into the city: no matter how it was (36) , it always seemed to get into and (37) the planes’ engines. (And yet the city needed salt to survive. ) And it is not good for nuclear reactors; the heat and the way that it came in, on water, meant that it (38) and crystallized around the uranium fuel rods. From the Times:
Crusts insulate the rods from the water and allow them to (39) up. If the crusts are thick enough, they can block water from (40) between the fuel rods. As the rods heat up, their zirconium cladding can rupture, (41) releases gaseous radioactive iodine inside and (42) even cause the uranium to melt and release much more radioactive material.
Getting fresh water in will (43) . Fresh, or rather bottled, water, is also (44) babies have been drinking as far away as Tokyo, after the levels of radioactive iodine 131 in the water there proved too (45) . (One preventative move is taking potassium iodide, commonly added to table salt here. ) This afternoon, there was (46) that the iodine 131 level had dropped below the official level of danger for babies—but since there wasn’t a very good explanation of how it got into Tokyo’s water in the first place, that was less (47) than it might have been. But it was an up-and-down day for the (48) at Fukushima Daiichi: two workers were injured when water, (49) with radiation, got into their boots. They are in the hospital now. There was also white smoke above two of the reactors. It’s not clear what that was (50) .