The correct option is
C consequently
Option A - 'However' means 'despite whatever amount/degree of something'. For example, 'I wanted that book, however, it was unavailable'. As the given sentence doesn't explain two different clauses, we can't use 'however' here. Thus option A is incorrect.
Option B - 'In that case' means 'in the situation of something.' It is used in a relatable clause. For example, 'If you still copy, in that case, I will have to suspend you'. As the given sentence doesn't have relatable clauses, we can't use 'in that case' here. Thus option B is incorrect.
Option D - 'This is because' is used to explain the reason. For example, 'This is because of you, that I'm suffering today.' The given sentence doesn't explain a reason, but a result, hence, we can't use 'this is because' here. Thus option D is incorrect
Option C - 'Consequently' is a conjunctive adverb which means 'as a result.' For example, 'I spend most of my money, consequently, I'm broke.' As the given sentence explains the result, we can use 'consequently' here. Thus option C is the correct answer.
'Marie didn't practice the piano; consequently, she played badly in the concert.'