1．(2019年北京卷·阅读理解D)Warming changes key ________ (character) of the ocean and can affect phytoplankton (浮游植物) growth.
2．(2019年天津卷·阅读理解C)Most food webs, for instance, consist of many weak ________ (link) rather than a few strong ones.
3．Absorbed ________ painting, John didn't notice evening approaching.
4．Our appetite for new products also contributes________ the problem.
