Final answer:
The approximate number of bacteria that can fit in 1 mm is 333.
Step-by-step explanation:
To find out how many bacteria can fit in 1 mm, we need to convert micrometers to millimeters. Since 1 millimeter is equal to 1000 micrometers, we can divide 1 mm by 3 micrometers to get the number of bacteria that can fit. Therefore, the answer is 333 bacteria, which is closest to option a) 300.