The correct answer is A - 'they are' - 'glasses' is plural. I say 'glasses is . .' because what I mean is that 'the word 'glasses' is . .' and 'word' is singular. Similarly this object [on the chair] is my grandma's glasses - object is singular. When we talk about the glasses as the subject 'they are on the chair'. 'Where are my glasses ?' 'They're on the chair.'

Technically, it should be "These ARE my grandma's glasses. THEY ARE on the chair." BUT Your sentence says "This is" so it means they want you to choose "it is." The truth is people often say "is" with glasses. That is, they making it singular. But technically it should be plural.

These are (plural) my grandma's glasses, they are (plural) on the chair.

A