this book is hard to read,這個是主動表被動的一種類型,相關(guān)知識點：在“be +形容詞+to
do”的結(jié)構(gòu)中,即不定式在作表語的形容詞后充當(dāng)狀語,同時,主語是不定式結(jié)構(gòu)的邏輯賓語,此時習(xí)慣上以主動形式表示被動意義.這些形容詞通常有difficult,
hard, cheap, expensive, enough, sure, fit, nice, dangerous, comfortable,
exciting, good, important等.例如: The text is easy to understand.這篇課文容易理解.
That article is difficult to write.那篇文章難寫.The chair is very
comfortable to sit on.這椅子坐起來很舒服.
一般說來,表示被動意義要用被動結(jié)構(gòu),但是,英語中也有以下幾種情況是用主動形式表達(dá)被動意義的：
某些連系動詞如look, sound, smell, taste, prove, feel等,習(xí)慣以主動語態(tài)形式表示被動的意義.例如：
The flower smells sweet.這花聞起來香.
Good medicine tastes bitter.良藥苦口.
The silk feels soft.絲綢摸起來很軟.
但是,當(dāng)上述動詞不用作系動詞時,則不具有這種用法.例如：His heart was felt still beating.他的心臟仍在跳動.
Pepper can be tasted in the soup.湯里有胡椒粉的味道.
當(dāng)open, close, shut, lock, move, read, write, wash, sell, clean, cook, burn,
draw, cut, wear, begin, start, finish, end,
keep等詞用作不及物動詞表示主語的某種屬性、特征或所處狀態(tài)（常與easily, quickly,
well等副詞連用）,而非強(qiáng)調(diào)動作本身時,通常用主動形式表示被動意義.例如： The table can’t move.這桌子移不動.
The door is easily locked.這門容易鎖上.The poem reads smoothly.這詩讀起來很流暢.When
does the concert begin? 音樂會什么時候開始?The peaches don’t keep
well.這些桃子不容易保存.
但是,有的時候也要看具體情況而定,例如：This book sells well. So far, 200 books have been sold
out.這種書賣得很好,到目前,已經(jīng)賣出了兩百本.The sentence was read clearly by
her.這個句子她讀得很清楚.
3. 在be worth doing, need / want / require doing (to be
done)結(jié)構(gòu)中,其后的動名詞一定是以主動語態(tài)的形式表示被動意義.例如：The book is worth reading.這本書值得讀.The plant
needs watering twice a week.這種花一星期要澆兩次.The baby wants looking
after.這個小孩需要照看.
4. 不定式to blame, to let, to seek用做表語時,通常用主動表被動意義.例如：Who is to
blame? 該怪誰呢?She was in no way to blame.決不應(yīng)該責(zé)備她.A better way is yet
to seek..還得找一種更好的辦法.
5. 在“be +形容詞+to
do”的結(jié)構(gòu)中,即不定式在作表語的形容詞后充當(dāng)狀語,同時,主語是不定式結(jié)構(gòu)的邏輯賓語,此時習(xí)慣上以主動形式表示被動意義.這些形容詞通常有difficult,
hard, cheap, expensive, enough, sure, fit, nice, dangerous, comfortable,
exciting, good, important等.例如: The text is easy to understand.這篇課文容易理解.
That article is difficult to write.那篇文章難寫.The chair is very
comfortable to sit on.這椅子坐起來很舒服.
6.
不定式作定語修飾名詞或代詞時（此時不定式與其所修飾的名詞或代詞之間存在動賓關(guān)系）,如果句子中的另一名詞或代詞（就是句子的主語）可以充當(dāng)不定式的邏輯主語,即與該不定式之間存在邏輯上的主謂關(guān)系,則此時不定式用主動形式表示被動意義.例如：I
have a meeting to attend.我有一個會議要參加.（其中I是不定式to attend的邏輯主語）Have you a
letter to send?你要去寄信嗎?（you是to send的邏輯主語）.
但是,當(dāng)不定式的邏輯主語與句子的主語不一致時,則不定式就需要用被動語態(tài).例如：Have you a letter to be sent?
你有信要我去寄嗎?（該句中不定式to be sent與主句主語you之間不存在邏輯上的主謂關(guān)系.）
7．在“疑問詞what/which/whom+不定式”結(jié)構(gòu)中,有時以主動形式表被動意義.例如：The question is which to
choose.問題是挑選哪一個.He will advise you what to do.他會建議你們做什么.
8. 在“too...to...”結(jié)構(gòu)中,用主動形式表示被動意思,此時不定式前面可以加邏輯主語.例如: The box is too heavy (for
me) to carry.這盒子太重了,搬不動.The room is not enough (for us) to have a meeting
in.這個房間不是大到足夠能在里面開會.