He had to retire(退休)early poor health.A. as a resultB. becauseC. soD. because of

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A. as a result
B. because
C. so
(答案→)D. because of
解析：as a result因此，结果是； because因为，接从句；so因此；because of因为，接名词性短语。句意：因为身体不适，他不得不提前退休。结合语境可知选D。