hi,
will the "comma" changed the meaning of the sentences?
Sentence1
I explained the questions in the exercise sheet during the first half of the class and then students would practise the questions during the second half of the class.
VS
I explained the questions in the exercise sheet during the first half of the class and , then, students would practise the questions during the second half of the class
Sentence 2
The new arrangement was that during the first 50 minutes students work on their exercises and I answer all questions one by one at the same time, whereas during the last 10 minutes I explained some most popular questions to all students
VS
The new arrangement was that, during the first 50 minutes, students work on their exercises and I answer all questions one by one at the same time, whereas, during the last 10 minutes, I explained some most popular questions to all students