Treatments for animals developed using animal testing include pacemakers for heart disease and hip dysplasia. animals后面为什么既有过去分词又有现在分词?过去分词和现在分词可以同时出现修饰一个单词吗?还有别的例子吗
...:I know here masks (are /is/ served / sold / saw/ seen) (as) one of the most common things
.翻译的大致意思是:我知道在这里,口罩是 /被视为最普通平常的事物,最容易买到、得到的事物。所以①括号里的助动词时态和数的问题:是用are/ is ...