question about gammar

兩句都不正確。It 在句中沒有antecedent, 後句 "when acid reacts with metal" 也不可用it作pronoun。由於任何一種acid和metal也可以有化學作用，所以要加上definite article。

你可以用被動式寫：
When an acid reacts with a metal, hydrogen is released.

問下以下2句句子邊句先岩?

1.It will release hydrogen when acid reacts with metal.- grammar is correct and better than no.2

2.It releases hydrogen when acid reacts with metal.= grammar is correct but no,.1 is better

第一句句子先岩.

1.It will release hydrogen when acid reacts with metal.

將英文翻譯成中文......

1.當酸同金屬產生反應時, 會釋放出氫氣。

2011-06-15 20:22:23 補充：
因為依一句句子係屬於Conditional sentence type 1.

Conditional sentence type 1 通常係用來表示一件事情可能會在依家或者將來發生。

2011-06-15 20:22:32 補充：
If-clause Main clause
---------------------------------------------------------------------------------------
If I don't have* any homework today, I will tidy** up my room.

don't have* If + present simple

will tidy** future tense "will"

2011-06-15 20:24:23 補充：
Correction, 係咁

If-clause Main clause
---------------------------------------------------------------------------------------
If I don't have* any homework today, I will tidy** up my room.

don't have* If + present simple

will tidy** future tense "will"