A. Age
Age is the best answer because it is easily determined and since there are stages of development, age can tell staff other things such as coordination level, ability and risk of getting hurt.
I'll go through the other answers briefly.
B. Intelligence. Intelligence is a fair enough answer, save for the fact that it is something that is not easy to determine quickly and hence, it would be difficult to determine each child's intelligence before they came into the daycare. Furthermore, intelligence or lack thereof does not necessarily mean that the child does not need as much supervision.
C. Previous training. This is not the correct answer because it is the previous training "of the children cared for." The children do not need to have previous training. It could work as an answer if it were in relation to the workers, not the children.
D. Coordination. Somewhat of a good answer. However, once again, coordination is not an easy determinant, and cannot always reliably predict how many staff should be with how many children.
Answer:
Taking the example of hand geometry, i-e fingerprints for verification, it is very easy to implement due to the relatively small size of the sensors. As with all digitally stored biometric data, there are risks of data theft.
Explanation:
Fingerprint sensors use scanners to scan the geometry of the patterns on the skin, usually the fingertips. These patterns are unique to each individual to a very high degree, roughly 1:64,000,000 pairs of fingerprints have the chance of being identical. These sensors are relatively easy to install, are cheap, and very user friendly. This makes this technique a very effective method.
Since the data collected by the scanners is almost always stored digitally in a device which is connected to the internet or has access points, there is always the threat of data theft which can result in identity theft and possible fraudulent activities.
The lens helps the eye to focus on images.
"The Lens. The lens is composed of transparent, flexible tissue and is located directly behind the iris and the pupil. It is the second part of your eye, after the cornea, that helps to focus light and images on your retina."
