[ Grammar ]
Other radioactive elements ______ since: actinium (Debierne), radiothorium and mesothorium (Hahn), ionium (Boltwood), etc.
A. were discovered
B. are discovered
C. have been discovered
D. had been discovered
Random Topics:
Quantifiers & Modals of ObligationArticlePhrase and ClauseQuestion Tagand, so, but, becauseso vs suchPassive and Active SentencesWas & Were QuestionsPronouns of QuantityHelping and Linking VerbsOther quiz:
Grammar › ViewA：What will you do tomorrow? B：I ＿＿＿ my dad ＿＿＿ the housework.
A. helped; to do
B. will help; do
C. will help; doing
D. helped; did
Vocabulary and Grammar › View
The social services are chiefly ________ with the poor, the old and the sick.
A. influenced
B. related
C. suffered
D. concerned
Present and Past Tenses › ViewI … for two hours before I twisted my ankle.
A. climbed
B. had been climbing
C. had climbed
D. was climbing
General Knowledge › View
Which is the smallest ocean in the world?
A. Atlantic Ocean
B. Gold Ocean
C. English Ocean
D. Tiger Ocean
E. Arctic Ocean