单选题 Janet Foster, who was ______ the president of the Riverside Corporation, has agreed to make the opening speech at the annual conference.
A. former
B. formal
C. formerly
D. formally

【正确答案】 C
【答案解析】选项(C)formerly是副词，意为“以前”。选项(A)former(以前的)和选项(B)formal(正式的)是形容词，不符合本题语法要求。选项(D)formally意为“正式地”，不符合本题语境要求。