Why do sociologists need to be careful when drawing conclusions from twin studies?
a) the results do not apply to singletons.
b) the twins were often raised in different ways.
c) the twins may turn out to actually be fraternal.
d) the sample sizes are often small

The answer to this question is D.The sample sizes are often small

Explanation:

1. state-issued photo ids. provide them for free for those who can't afford them.

2. the system we have seems to be working nearly perfectly. seems like about 31 cases per billion votes cast

3. the national policy for hiring new employees which requires proof of eligibility to work. there are something like 20 types of identification which can be used for this.