若等差数列{a_n}中，a₁＞0，S_n表示数列的前n项和，且S₄=S₈，则S_n取最大值时n=______．

The president _____ all people _____ our environment.         [ ]

A. urge; protect

B. urged; to protect

C. urges; protect

D. urged; protect