―What’s the matter? You look worried and restless.―Oh nothing really serious. As a matter

问题补充：

―What’s the matter? You look worried and restless.

―Oh, nothing really serious. As a matter of fact, I of my graduation thesis. I have to hand it in soon.

A. am just thinking

B. just thought

C. have just thought

D. was just thinking

答案：

A. am just thinking

B. just thought

C. have just thought

(答案→)D. was just thinking

解析：考查动词的时态与语态。从会话可知，答话人是在解释他look worried and restless 的原因，因为他（刚才）是在思考毕业论文的事，这是说话前的那个时刻正在发生的事情。故应用过去进行时描写正在进行的动作。