no
This is a controversial topic. Most would say parents should not be allowed to choose the gender of their child because it will lead to gender imbalance and abortions.
no, because if it was it wouldn't be science anymore, it would just be one general subject with sub-subjects, so that would defeat the purpose of subjects if there is only one
Beijing has a questionable record on human rights and many people believed that they should not be allowed to host this type of international event.
You should use "they do" with plural subjects, such as "they do their homework," and "does" with singular subjects, like "she does her chores."
controversial issues
This is a controversial issue. Some people, and certainly the government, seem to believe they should be allowed to stay. Many citizens believe if they entered the country illegally they have already broken the law and should be sent back to their own country; however, there are those who do not agree with that. Some believe they should be granted amnesty and others disagree.
No, except at the beginning of a sentence because it is n ot a proper n ou n.
ddsf
Three common signs of dyslexia that parents and educators should be aware of are difficulty with reading fluency, struggles with phonemic awareness, and challenges with spelling and writing.
There are truly no reasons as to why FaceBook should not be allowed.
I believe we should be choosing our subjects
Your question requires a lot more information before it can be answered. We do not know which subjects you are talking about, or why there should be a limited number of subjects.