1//It is not just imagery that offers this impression, but the tendency for magazines to blur the boundaries between the purpose of text, image, expert advice, and ads increases over time in our ten- year sample.

其中的and和谁是并列的？increases 为什么用单数动词形式… 

【答】上句为并列句。第一分句为“强调结构”；第二分句的主干是：

1. the tendency （主语）increases （谓语）over time in our ten- year sample.（时间状语）

2. for magazines to blur the boundaries between the purpose of text, image, expert advice, and ads：这是“不定式的复合结构”（即：“带有逻辑主语的不定式”）：for sb/sth to do sth.

3. adds 跟前文的between the purpose of text, image, expert advice并列，前面由and连接。

2//The images merge seamlessly in the magazines from article to ad and back again.

其中back 是动词还是……副词？

【答】back 是副词表方向，意为“返回”。back again 意为“再返回来”。具体到本句，前面是from article to ad “从文章到广告”，back again 的意思就是“从广告到文章”。也就是把“from A to B”颠倒过来再说一遍。又如：

She stood there looking from the fish to the boy and back again.

她站在那里，从鱼儿看向男孩，然后又看回去。（从男孩看向鱼儿）