because引导的原因状语从句一般放于主句的后面，because从句位于句首时要用逗号分开，放在句末时，可不用逗号分开。because表示直接原因，语气最强，最适合回答why引导的疑问句。
because引导原因状语从句（1）Because he is my friend，I believe him.
因为他是我的朋友，（所以）我相信他。
（2）I believe him because he is my friend.
我相信他，因为他是我的朋友。
（3）Because it is an area of outstanding natural beauty, you can't build on it
考虑到这一带自然风光旖旎，你不能建在这里。
（4）Because the traffic is so busy, she failed to arrive at the station on time.
因为路上交通太拥挤，她没能准时赶到车站。
because从句与because of短语的转换Because引导的原因状语从句有时可与because of 短语转换，because of后加的原因可以为好或坏，但最正规的还是because。
（1）He can't come because he is ill./He can't come because of his illness.
他因病不能来。
（2）I said nothing about it because his wife was there./I said nothing about it because of his wife's being there.
因为他妻子在那儿，我对此事只字未提。
