1. 用 need not 出自以下几个方面的原因：
1） 表示“建议”的 suggest 后的宾语从句要求用虚拟语气 （should + 动词原形——should 可以省去,直接用动词原形）
2） 这里的 need 是情态动词,而情态动词是没有人称变化的.
3） 如果把 need 用作实意动词,需要改为 （should）not need to limit.
关于 need 的用法
1）实意动词：后面只能跟动词不定式,即 need to do,具体用法如下：
肯定 —— need to do sth.
否定 —— don't/doesn't need to do sth.
疑问 —— Do /does... need to do sth.?
2) 情态动词：只用于否定、疑问和条件从句,具体用法如下：
否定 —— need not do sth./ needn't do sth.
疑问 —— Need ... do sth.?
条件从句 —— If ... need do sth.
2. The Roman poet Virgil is highly esteemed today for his epic poem, The Aeneid, yet on his deathbed he himself sought to prevent its publication on the grounds （of not being） sufficiently polished.
句子的意思是“罗马诗人维吉尔由于他的史诗《埃涅伊德》在当代被高度评价,然而,他本人在临终只是曾以没有（被别人）充分润色为由而设法阻止这部诗歌的出版.”
从翻译可以看出,本来润色是由维吉尔去做的,但是此处却成了别人做的,因此不应该用动名词的被动语态,而应该改为主动：on the grounds of not making it sufficiently polished.
其中——
on the grounds of doing sth. 表示“以...为理由”
make sth. polished 使得某物精炼
如果把后半句改动如下即可一目了然：
he himself sought to prevent its publication on the grounds that he had not make it sufficiently polished.（it 指代 publication,用作宾语；sufficiently polished 是过去分词作宾语补足语）.
3. A thick growth of sunflowers stood ten feet tall, their brown heads drooping over the fence with the weight of their seeds.
1） A thick growth of sunflowers stood ten feet tall 是本句的主题,意思是“向日葵的茁壮生长都足有十英尺高”.
2）their brown heads drooping over the fence with the weight of their seeds. 是独立主格结构作陪衬形状语,意思是“带着果实的重量,褐色的花头一直下垂到篱笆上”.
这个句子只能意译,不然就会成了不合汉语习惯的句子：
向日葵茁壮地生长,每一株都足有十英尺高,那褐色的花冠由于果实的重量而一直低垂到篱笆上.