Answer is A

Answer should be A

Answer is A : combine the two SELECT statements into a single SOQL statement
List<Account> aList = [SELECT Id, (SELECT Id FROM Contacts) FROM Account];
for(Account acct : aList){ //todo }

Answer is D.
For loop can be replaced by the query: [SELECT Id FROM Contact WHERE AccountId IN :aList]

B is wrong - you can add too high LIMIT to the first SOQL and then still hit the governor limits in for loop.

Answer is B.