If you__ see James,ask him to phone me ,为什么用should?

if you should see James,ask him to phone me.这里为什么填should?为什么 Please ask him to see me.为什么要加to? If ___ calls me when I am out,ask him to leave his phone num ( )、if somebody comes to see me,ask him to leave a --------- If by any chance someone comes to see me ,ask him to leave a Ask him to ring me up if you ____________ him. i'm busy now,ask him to see me _other_time If someone calls me, ask him to leave a ______. If someone calls me,ask him to leave a______答案 Peter（ ）phone.if he does,could you ask him to ring later?(ca if_ calls me when i am out,ask him to leave his phone number Ask him to call his office as soon as possible if you should