单选题4.______ the calculation is right, scientists can never be sure that they have included all variables and modeled them accurately.
【正确答案】
A
【答案解析】本题测试：连词的区分。四个选项的含义分别是：A项even if“即使；即便，哪怕”；B项as far as“(表示程度，范围)就……；至于……”；C项if only“只要；要是……多好”；D项so long as“只要”。根据主句句意：“科学家也永远无法确保……”空格处应选用even if，构成让步从句，意思是：即便计算是正确的，科学家也无法确保……C、D项构成条件从句，不妥。