Question:
Students are not allowed to handle these chemicals unless they _________ under the supervision of a teacher.
-
A.
are -
B.
were -
C.
have been -
D.
had been
Reference explanation:
Correct answer: A
Answer A
Knowledge of conditional sentences
Based on the simple present tense in the main clause being divided “are not allowed”, we infer that this is a conditional sentence of type 1.
=> choose option A
=> Students are not allowed to handle these chemicals, without teacher supervision.
Other structures to note:
Allow/permit sb to do st = let sb do st: allow someone to do what
Allow/permit doing st: allow to do
Be allowed/permitted to do st: what is allowed
Be under the supervision of sb: under someone’s supervision
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