题目内容：
根据下列文章,请回答题。Healthy FoodStreet sellers，particularly in developing countries，supply large amounts of food________(51)people on low incomes．This sector(部门)also employs some 6-25%of the work force，mainly women。in developing countries，and provides markets for agricultural and other produce．In many countries，________ (52)，the authorities are not willing to recognize it as a formal sector of the food________ (53)system；they may ignore it in food control programs or even try to put an end to________ (54)．There are two possible contaminants(污染物)：pathogenic(病原的)micro-organisms (微生物) ________ (55)harmful chemicals．As________(56)as micro-organisms are concerned，there is apparently no convincing evidence that street foods are more involved in the transmission of infection than foods obtained in。e．g．hotels．Studies in Egypt and elsewhere have found street foods to compare not unfavorably with hotel
________ (57)in respect of contamination with micro-organisms—some street foods were found to be contaminated with pathogens(病原菌)，but SO were foods from four—and five-star________ (58)in the same area．
Harmful chemicals have been found in street foods．and food exposed for sale on roadsides may become________ (59)by lead from vehicle exhausts．
Health dangers may arise Purchase of raw materials of________ (60)quality：improper storage，processin9，and cookin9，leading________ (61)reuse of water；limited piped drinking-water；lack of refrigeration(冷藏)：Unsatisfactory waste—disposal facilities；and personal cleanliness．
The authorities should________ (62) into account the potentials of different categories of food for transmitting disease，and should set appropriate standards of control for the different categories—sellers of bottled drinks require less control than those of food, Dry foods, dried grains，and sugared foods are________ (63)likely to transmit disease than cooked rice，low—acid milk，egg。and meat products________(64)。Foods which are thoroughly cooked and eaten at________(65)are safer than precooked food kept at high temperatures for several hours． A．for
B．on
C．by
D．at
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