Please come to our house one day and have a ------ with us.

选c.
随便吃顿饭的意思.dinner是一天当中的正餐.如果请别人吃饭,只能轻描淡写地说啊,不能说我请你到我家,吃顿正餐,好像中外都不这么说.
再说,如果 有a ,还要用dinner,就不是一个词了.have a good dinner要不就只能说have dinner.