某课外兴趣小组的同学所做的下列四个实验，符合如图所示图象的是______．

①在稀盐酸中加入适量的碳酸钠

②把生锈的铁钉放入过量稀硫酸中

③将氯化钠溶液和硝酸银溶液混合

④在氯化铁和稀盐酸的混合溶液中加入氢氧化钠溶液．

I always have so many things to ________ when I come into the office after a trip abroad.

A．add to

B．attend to

C．contribute to

D．appeal to