122. Melina Kunar of the University of Warwick, and Todd Horowitz of Harvard Medical School ran a series of experiments in which two groups of volunteers had to pay attention and respond to a series of moving tasks on a computer screen that were reckoned equivalent in difficulty to driving.

译文　

华威大学的梅利娜·库娜和哈佛医学院的托德·霍罗威茨做了一系列试验，他们让两组志愿者注意电脑屏幕上的一系列移动任务并作出反应，这些任务被认为与开车的难度相当。

点睛　

本句的主干是Melina Kunar...and Todd Horowitz...ran...experiments...。其中，in which two groups of volunteers...to driving属于“介词＋关系代词”引导的定语从句，修饰先行词experiments，该从句中又包含一个that引导的定语从句，修饰先行词moving tasks。
reckon意为“认为”，此外它还含有“考虑；估计”之意。如：
I have to reckon the cost before I book the tickets. 我得先算一下费用，然后再订票。
equivalent意为“相等的；相当的”。如：
This qualification is equivalent to a degree. 这个资格证书相当于学位证。

考点归纳　

由“介词＋关系代词”引出的定语从句须注意以下几个问题：
关系代词which和whom在定语从句中作介词的宾语时，介词可放在关系代词之前，也可放在该定语从句中的动词之后（此时，which可用that代替，whom可用who或that代替。在口语和非正式文体中，关系代词可以省略）。如：
I'm looking for a friend with whom I can chat on msn. 我在寻找一个能和我用msn聊天的朋友。
此句可以改为：I'm looking for a friend (who/whom/that) I can chat on msn with.
关系代词that在定语从句中作介词的宾语时，介词只能放在从句中de相关动词之后，不可放在that前面，但that可省略。如：
The position(that) she applied for is very attractive. 她申请的那个职位很有吸引力。（√）
The position for that she applied is very attractive. (×)
在由“代词＋of＋关系代词”结构引导的定语从句中，先行词指“人”时用whom,指“物”时用which。如：
There are 50 students in my class, most of whom are girls. 我们班上有50个学生，其中大多数是女孩。
He has a large collection of books, many of which are written in English. 他藏书很多，大部分是英文书。