此题为什么选B？
这题选B是对的。
有必要区别一下这几个选项。
so as to = in order to，其否定式 so as not to = in order not to，例如：
(1) I always keep fruit in the fridge so as to keep insects off it.
（我总是把水果放冰箱里，以便防虫。）
(2) He did not switch on the light so as not to disturb her.
（他不开灯，目的是不想打扰她。）
such as to 表示“如此（...）以至于”，其中such 是代词，能作表语，具体代替的东西要看上下文。例如：
(3) His remarks were such as to annoy everybody at the meeting.
（他讲话如此（冒失），以至于到会的人都心有不快。）
such that的意思和such as to相近，也能作表语，但用法不同，因为that后面要接从句。例如：
(4) Our lunch was such that we don't really need an evening meal.
（我们的午饭如此（丰盛），以至于我们都不怎么想吃晚饭了。）
so that 的意思和so as to 相近，但so that 也是后接从句。如：
(5) Leave the keys out so that I remember to take them with me.
（把钥匙拿出来，好让我记得带上。）
可见，只有such as to 能满足题目的2个要求：
1）在系动词was后面作表语
2）后接动词而不是从句
此外，还需要注意so ...as to, so...that, such ...as to, such ...that的用法。例子：
(6) The word itself is so rare as to be almost obsolete.
（那个单词本身属于生僻字，几乎没有人用了。）
(7) The story was so touching that we were moved to tears.
（那个故事很感人，结果我们都感动得哭了。）
(8) Tom was such a fool as to believe him.
（汤姆够傻了，竟然相信了他。）
(9) I tried to tell her in such a way that she wouldn't be offended.
（我尽量以一种（委婉的）方式告诉她，使她不受到刺激。）
