Because of the Russian gas limit to Europe attempts to use botanical fuel as a source of

问题补充：

Because of the Russian gas limit to Europe, attempts to use botanical fuel as a source of power.

A. have made

B. having made

C. are being made

D. will be making

答案：

A. have made

B. having made

(答案→)C. are being made

D. will be making

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