agreement

" Was " is used in the sentence because " revealed " is in past tense, so naturally " was " is used, as the above has pointed out.

However, this sentence does not have to be written in past tense alone. It can be written in present tense, as most people do, since the investigation is like all reports, is valid at all times, though it is about the past. When we talk about books and reports alike, we often use present tense to talk about the data and facts as presented in the books and reports. A mixture of present tense and past tense and future tense is also possible.

The commissioner shall issue a notice of revocation of registration to a contractor when an investigation reveals that the contractor no longer meets the conditions of registration set out in section 48-2105 by failure to maintain ...
assist.neded.org/contrctr.html - 17k -

Present tense is used in the above.

As soon as an investigation reveals that Caller ID rewriting was integral to some type of "terrorism," the industry will find itself at the wrong end of an even more poorly written legislative cannon that will crush companies and ...
www.oreillynet.com/pub/a/etel/2006/10/18/solving-the-caller-id-problem.html - 26k -

Present tense + past tense + future tense

" Reveals " is often in present tense, whereas the things being talked about in the report can be in past or present tense.


" Abuse " is the main subject here. " Was " is used because " abuse " is in singular. However, if the plural form " abuses " is used, then the plural form " were " or " are " will be used.

The abuses of alcohol and drugs were merely a ploy introduced by the DNC and NEVER supstantiated to ANY degree. You simply reinforce your stupidity with assumtions you make up to try and reinforce your pipe dreams. ...
www.sysopt.com/forum/archive/index.php/t-172386.html - 68k -

In fact, this sentence can be written in present or past form, in singular or plural.

2006-11-23 18:19:17 補充：
用中文解解， ABUSE 可以是單數或眾數，如眾數 ABUSES 便要用 ARE。INVESTIGATION 可以是 PAST 或 PRESENT TENSE， 所以如果是現在式便要用 IS。多數 REPORTS 會用 PRESENT TENSE，因那份報告是不會消失，所說的資料亦是有效。問題是你的例句是如此，所以找出個 MAIN SUBJ 是 ABUSE， 而不是後面那堆，所以才用 WAS， 因為前面用了 REVEALED ，所以才用 WAS， PAST TENSE。

2006-11-23 18:20:42 補充：
其實現在過去都可以用，但最好是前後一致，特別是校內作文。

1. "abuse of alcohol and drugs" 濫用酒精和藥物這件事 是指一件事,所以動詞用單數 ,用is 代替 are ,雖然你見到drugs這個字有s,但基於 "abuse of alcohol and drugs"是指濫用一事,所以是用單數表示,
2. 因為investigation (研究)revealed (揭示) ,是做完研究才能揭示出結果,因此一定是用過去式,既然是過去,所以不用is,而用is的過去式 was,所以句子用was。
圖片參考：http://hk.yimg.com/i/icon/16/18.gif