_______cloning human embryos is not legal in many countries, some scientists are already pushing ahead with research in order to produce a cloned human baby.
A．WhileB．WhenC．SinceD．if only
A

試題分析：考查連詞：A. While雖然,B. When當…時候，C. Since既然D. if only 但愿，句意：雖然克隆人類胚胎是違法的，但一些科學家已經(jīng)在努力推進研究為了制造克隆的人類嬰兒。選A。
點評：考查連詞主要是弄清每個冠詞本身的含義，做題時一定要根據(jù)上下文的邏輯關系選擇。
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