He didn't go to school yesterday ________ he was ill.
A：because
B：because of
C：if
D：so
“通过封建契约和分封仪式，如臣服礼、授职礼，领主和附庸形成依附关系。”材料体现的制度是（ ）
----- How long can I ______ the book? ------ Two weeks.
