Not until I began to work ________how much time I had wasted．

B
B 【解析】本题考查句子的部分倒装结构。当not…until置于句首时，句子要使用部分倒装，即将谓语的一部分如助动词或情态动词放在主语之前。如果句中的谓语没有助动词或情态动词，则需添加助动词do、does或did，并将其置于主语之前。本句正常语序为：I didn’t realize how much time I had wasted until I began to work．