-We have not heard from him for a long time .

选C.do you suggest在这里做插入语,可以看做省略,根据题意要用现在完成时,do you suggest与do you think,do you suppose用法一样,后两者同样可看作插入语
Happen 用法小结
生活中什么事都可能会“发生(happen)”.那么,你知道怎样使用happen这个词吗?下面我们就对happen的用法作一小结.
happen是不及物动词,它的用法常见的有如下几种情况：
1.表示“某地(某时)发生了什么事”,常用“sth.+ happen +地点/时间”这一结构来表达,此时主语应是事情.例如：
The story happened in 2003.这个故事发生在2003年.
An accident happened in that street.那条街上发生了一起事故.
2.表示“某人出了某事(常指不好的事)”,要用“sth.+ happen+to sb.”这一结构来表达.例如：
A car accident happened to her this morning.今天上午她发生了交通事故.
What happened to you?你怎么啦?
3.表示“某人碰巧做某事”,要用“sb.+ happen+ to do sth.”这一结构来表达.例如：
I happened to meet a friend of mine in the street yesterday.昨天我碰巧在街上遇到了我的一个朋友.
4.happen表示“碰巧或恰巧发生某事”时,还可用“It happens / happened that...”这一结构来表达.例如：
It happened that Brian and Peter were at home that day.碰巧那天布莱恩和彼得在家了.
It happened that he had to take part in a meeting that afternoon.碰巧那天下午他不得不参加一个会议.
注：that从句中的主语是人时,此种结构可以与“sb.+ happen + to do sth.”结构互换.例如：
It happened that Brian and Peter were at home that day.= Brian and Peter happened to be at home that day.
suppose如何用
suppose的基本意思是“猜想；以为；假定”,但在具体的语言环境中意义不止于此,其用法如下：
1.suppose + that 从句,表示“猜测；假定”.如：
I suppose that you are right.我想你是对的.
You can suppose that A equals B.你可以假定A等于B.
2.suppose +名词 / 代词 + to be...,表示“认为……是……”.如：
Many people suppose him to be over 50.许多人认为他已经50多岁了.
3.suppose用于祈使句中,表示“让……”.如：
Suppose we go for a swim.(= Let's go for a swim.) 让我们去游泳吧.
be supposed to 的用法
用法一：be supposed to...其中to是动词不定式符号,不是介词,其后要跟动词原形.当be supposed
to...的主语是“人” 时,意为“应该……
”；“被期望……”,它可以用来表示劝告、建议、义务、责任等,相当于情态动词should.如：
Everyone is supposed to wear a seat-belt in the car.
每个人在汽车里都应该系安全带.
Teachers are supposed to treat all the students alike.
老师应该对所有的学生一视同仁.
用法：当be supposed to...的主语是“物”时,它表示“本应；本该”,用于表示“某事本应该发生而没有发生”.如：
The new laws are supposed to prevent crime.这些新法令本应该起到防止犯罪的作用.
The train was supposed to arrive half an hour ago.火车本应在半小时之前到达.
用法三：be supposed to后面接“have + 过去分词”时,表示“本应该做某事而没做”.如：
You are supposed to have handed in your homework by now.
现在你应该已经把作业交上来了.
He is supposed to have arrived an hour ago.他应该一小时前就到了.
用法四：be supposed to...的否定结构为be not supposed
to...,它常用于口语中,意为“不被许可；不应当”.如：
She was not supposed to be angry about that.她本不该为那件事而生气的.
You are not supposed to smoke on the bus.你不应该在公共汽车上吸烟.