In order to establish the expiration date of perishable food, growth curve data must be collected. Once the microbial load is so high that it poses a hazard to human health, the food item is no longer considered safe (expired). Generally a load of x50,000 bacteria/gram is considered unsafe. Your task is to determine the microbial growth curves for MicroYo, a new brand of yogurt. The growth is determined by sampling the yogurt and growing the bacterial isolates in broth culture which is then serially diluted by a total of x10,000 and inoculated onto standard petri plates of nutrient agar. The following colony counts are measured. Based on this data and considering the information in the paragraph above regarding safe levels, Please choose the last possible day to enjoy the yogurt before there is a dangerous level of bacteria:

Time (days) Micro Yo colony count #
1 1
4 1
12 2
16 4
20 7

a. 4
b. 16
c. 20
d. 12