【正确答案】 A

【答案解析】[解析] 原文第一段第三行说到“I believed he had a hard life as a child， and I know that he left school at the age of ten and started work．This may have had something to do with it，but I can only guess，”(我相信他的童年一定很艰难，我还知道他十岁就离开学校去千作了．这可能跟他的难以接近有关，但我也只是猜测)，这里关键词是“This may have had something to do with it”中的两个代词“this”和“it”。通过上下文我们得知this指代爸爸的童年经历，让指代爸爸难以接近的特点。所以本题的命题“爸爸不善交际是由于他不快乐的童年”为正确。