Usually John _____ to school in his father's beautiful car.[ ]

A. has taken

B. is taking

C. is taken

D. has been taken

《大明律·名例律》规定：“凡律自颁降日为始，若犯在已前者，并依新律拟断。”其注云：“此书信犯罪在先，颁律后事发，并依新定律条拟断，盖遵王之制，不得复用旧律也。”
请说明其基本含义，并从法律适用原则发展变化的角度，分析这一规定的历史背景及主要目的。