Scientists ___________ Mars for decades, searching for signs of life.
A. were exploring
B. have explored
C. was exploring
D. has explored

Random Topics:
Subject and Verbs AgreementAdverbs of frequencyPresent tense AffirmativeModals and TensesConditionals Type ILinking Verbs and TensesPronouns/ Present TenseAdverb of Frequency and TensesThe Structural Types of SentencesPersuasive TextOther quiz:
Tenses › ViewMy father ___________ me to help him last Sunday.
A. asked
B. was asking
C. asks
D. will ask
Modal Verbs › View
The construction crew might ________ the bridge in time for the holiday traffic.
A. finished
B. to finish
C. finish
D. finishing
Grammar › ViewWhich sentences is/are correct?
1. Prince William Bridge, built in 2012, is the newest in the city.
2. There’s a Japanese death metal band playing at the club on Saturday.
3. The house overlooked the valley has gorgeous views.
A. 1,2,3
B. 3
C. 1,2
Tenses › View
Shaka : Jake, I bring you a souvenir from Bandung.
Jake : Oh my God. It is too cute. You know what I like.
Shaka : Sure, you are my best friend.
Jake : ___
Shaka : Don’t mention it.
Complete the dialog above ___
A. Thank you very much
B. I am sorry
C. See you
D. Really?
