tests by here4u with the online test builder (650 tests)

501. I'd better... I'd rather... (24003 candidates)
502. When : What tense to put behind... (31926 candidates)
503. Vocabulary: Animal sounds/cries (12423 candidates)
504. Vocabulary: Emergency - First aid... (29031 candidates)
505. Expressing time: by... , by the time..., once... (5969 candidates)
506. Before - In front of - Opposite... (8575 candidates)
507. Vocabulary: Swimming, diving... (2714 candidates)
508. Who - What - Which (24353 candidates)
509. Infinitive implied by its particle. (3368 candidates)
510. Doing, Do, To do... (9390 candidates)
511. Choosing your past tense... (47934 candidates)
512. Tenses : satisfying the request... (2) (2185 candidates)
513. The use of tenses: a strange request...(1) (3620 candidates)
514. Either...or/ Neither...nor/ Not ... either. (13481 candidates)
515. There is / are, and other forms... (5076 candidates)
516. To be / to have: -ing forms... (4305 candidates)
517. Enough with the Present Perfect... (21860 candidates)
518. Whose and use (5461 candidates)
519. Else and compound words (3728 candidates)
520. What, which and all that (7027 candidates)