在Fe₂(SO₄)₃溶液中，加入a g铜，完全溶解后，再加b g铁，充分反应后得到c g残余固体，且a>c，则下列说法正确的是[ ]

A．残余固体是铜和铁

B．最后得到的溶液中一定含有Cu²⁺

C．将残余固体加入到稀硫酸中，有气泡产生

D．最后得到的溶液中可能含有Fe³⁺

The () sound of movements in the kitchen suggested that the children were secretly helping themselves to the chocolate cake.

A. faint

B. vague

C. slender

D. dim