Explaining
• We have considered ...
• We have looked at ...
• There are two alternatives ...
• The first option is to ...
• There are two reasons/explanations for this. First ... Second ...
• This is/can be explained by two factors. First,... Second, ...
• This is due to ... and also to ...
• One reason for this is ...
• Another reason is ...
• One way to solve this problem is ...
• Another is to ...