Heboughtahouseforhischildren________
B
本题属于动词不定式复合结构做后置定语。 in 不可省略。句意：他买了一套房子给孩子们住。
The traffic was held up for more than thirty minutes, ________ caused me to arrive late.
Sofarscientistshaveonlyacquired________understandingofthephysicalprocessesthatcauseearthquakes.