Answer :
Option A is correct.
"We have to master the routine during this morning's practice; otherwise, the coach says we will have to work a second (II) day."
"otherwise, the coach says we will have to work a second (II) day" is telling why they have to master the routine; therefore a semicolon is used.
"We have to master the routine during this morning's practice; otherwise, the coach says we will have to work a second (II) day."
"otherwise, the coach says we will have to work a second (II) day" is telling why they have to master the routine; therefore a semicolon is used.