7.引导原因状语从句的从属连词有 because, as, since等。

because“因为”语气最强,回答why提问时只能用because，其引导的从句可放在句首或句末;as“由于”、since“既然”语气不如because强，引导的从句常置于句首;for是并列连词，语气最弱，对前面分句加以解释或补充说明，其引导的分句常置于句末且用逗号隔开。

He didn’t go to school because he was ill.

As it was raining, we went there by bus.

Since everybody is here, let’s begin.

It must have rained last night, for the ground is wet.

注意： because与 so不能同时使用。

8.引导让步状语从句的从属连词有：although/though(虽然，尽管), even though/if (即使)

Although/ Though it is a very young country, it is very rich.

Even if/ though you were here yesterday, you couldn’t help him.

注意：although/though 引导的从句不能与but连用，但可与yet, still连用。

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