Because blood from different individuals may different in the type of antigen on the surface of the red cells and the type of antibody in the plasma, a dangerous reaction can occur between the donor and recipient in a blood transfusion. 

She has disappeared three days ago, and they are still looking for her now.

Neither his parents nor his teacher are satisfied with his result when he was at school.

The amount of women earning Master's Degrees has risen sharply in recent years.

People are not allowed enter the park after midnight because of lack of security

If you need to keep fit, then why not take on a sport such as badminton or tennis?

There is a severe famine in Somalia, and thousands of people are dying from hunger.

Dinosaurs became extinct millions of years ago because of the earth's climate changed drastically.