What is this in English? “这用英语怎么说?”可以回答是It is a telephone. 在英语中叫“a telephone”根据疑问句中this（表单数）,本来就要对应地用单数回答,肯定要用a telephone来回答；但如果你问What are these in English? 你的回答就应用复数来回答,用They are telephones.
简单问题不要复杂化.