单选题 The tremendous heat at a star's core, ______ tremendous gravity, joins the nuclei of hydrogen atoms.
A. combined with B. having combined with
C. combining with D. being combined to

【正确答案】 A
【答案解析】[解析] combined with此处表示一种一般情况，相当于when (it is) combined with，所以无需时态变化。