It be essential that 后面一定用虛擬語氣，且句子謂語動詞固定為(should) + 動詞原型;

　　It was essential that the applications forms send back before the deadline.

　　53. We _D_ our breakfast when an old man came to the door.

　　A just have had B have just had C just had D had just had

　　when 還可以表示①剛..就… (有動作先后關系)、②恰在此時;

　　44. I had just started back for the house to change my clothes _D_ I heard voices.

　　A as B while C after D when

　　45. I felt somewhat disappointed and was about to leave, _C_ something occurred which attracted my attention.

　　A unless B until C when D while

　　64. It was essential that these application forms _D_ back as early as possible.

　　A must be sent B will be sent C are sent D be sent

　　非謂語動詞與獨立主格：短語，句子(或者句子，短語)

　　1.當短語部分有獨立主語，并且該主語不同于句子主語，這時短語結構稱為獨立主格。(它最明顯的特點是短語部分有獨立的主語)。

　　獨立主格的結構1：名詞(代詞)+ 分詞 [現在分詞、過去分詞]

　　現在分詞表示主動的，正在進行的行為;過去分詞表示被動的，已經完成的行為。 作題時要通過判斷動作與名詞(代詞)之間的關系來確定是使用現在分詞還是過去分詞。當動作由名詞(代詞)發出時使用現在分詞，而名詞(代詞)是受動者時則用過去分詞。

　　54. Silver is the best conductor of electricity, copper _B_ it closely.

　　A followed B following C to follow D being followed

　　49. All things _A_, the planned trip will have to be called off.

　　A considered B be considered C considering D having considered

　　call off 取消; cancel vt. 取消; 四級中的考點就是現在分詞和過去分詞的區別。

　　獨立主格的結構2：with + 名詞(代詞)+ 分詞 [句子當中作狀語]

　　36. After the Arab states won independence, great emphasis was laid on expanding education, with girls as well as boys _C_ to go to school.

　　A to be encouraged B been encouraged C being encouraged D be encouraged

　　as well as 和(相當于and); be encouraged不會考。

　　動詞不定式有預示將來行為的含義。to be encouraged 將要被鼓勵;

　　been encouraged 已經被鼓勵完了，與主句的謂語動詞相對;being encouraged 正在被鼓勵

　　2.短語部分沒有獨立主語，則短語結構稱為非謂語動詞。

　　非謂語動詞的結構：分詞(分詞短語)

　　句子的主語決定非謂語動詞中的分詞是用主動還是被動形式。如果是句子的主語發出動作，則使用現在分詞;如果動作不是由句子的主語發出，則使用過去分詞。