Robert is said ______ abroad, but I don't know what country he studied in.
     A. to have studied              B. to study 
     C. to be studying               D. to have been studying
    考查不定式的时态，注意题干中的studied in这一关键词所提供的信息时态，说明Robert已去国外学习过了，故该题用不定式的完成式，表示不定式的动作先于谓语词的动作，所以答案选A。
     1．常见的可接不定式完成式的动词有：seem, appear, happen, prove, pretend等。如：
The beggar seems not to have eaten anything.这乞丐似乎没吃过东西。
She seemed not to have grasped what he really meant.她看来没有明白他真正的意思。
     2．常用于“主语+be said +to have done, been”相当于主动句“People say +that”结构的句型有：be said, reported, thought, supposed, expected, believed considered, known.如：
Charles Babbage is generally considered to have invented the first computer.普遍认为查理斯·巴别基是发明电脑的人。
She was said to have met a fairy one day.据说有一天她碰到了一位仙女。
     3．常见的可接不定式完成的形容词有：glad, happy, sad, disappointed, satisfied, likely, sorry, surprised等。如：
She is not likely to have got our letter. (=It is not likely that she has got our letter.)她可能还没收到我们的信。
    比较下面的不定式的一般式和完成式的区别：
I'm happy to have seen you.见到你很高兴。（道别时说）
I'm happy to seen you.见到你很高兴。
I'm sorry to have kept you waiting for a long time.对不起，让你久等了。（说话时已等了很久）
I'm sorry to keep you waiting for a long time.对不起，要让你久等了。
     4．在would like, love, rather后面用不定式完成式，表示想做而未做的事情。例如：
I would love to have gone to the party last night but I had to work extra hours to finish a report. (=I would have loved to go to the party last night but……)我原打算昨晚去参加聚会，然而我不得不抽空写一份报告。
I'd like to have seen his face when he opened the letter. (=I'd have liked to see his face when……)我真想看见他拆信时的脸色。
    [注意]  这类表示“意图、打算”之意的动词，还有hope, wish, expect, think, suppose, want, plan, agree, mean, try等用过去时态，后又接不定式完成式作宾语，表示想做而未做的事情。这种意义也可用这类动词的“过去完成时态+不定式的一般式”表达。
We hoped to have caught the early bus, but found it had left. (=We had hoped to catch the early bus, but……)我们本来希望赶早班车，却发现车子已经开走了。
I planned to have attended the meeting last night, but someone called and I couldn't get away. (=I had planned to attend the meeting last night, but……)我昨晚本来计划去开会的，但有人找，脱不开身。
     5．be+不定式完成式表示该做或想做但未做的动作。如：
You were to have arrived there early that day. 那天你们应该早点到那儿。（但你们晚到了）
I was to have helped him then, but was too busy.当时我本想帮他的忙，可我太忙了。（未帮他的忙）