Complete the sentences with the modal verbs below: can/can't/could/couldn't /wasn't able to, may/might or have to/had to. 1. people write e-mails until 1990. since then they have written billions of them. 2. unfortunately, i really program at all. no-one among my friends is a programmer either. 3. i send my e mail from yahoo mail. there were some problems with the server. 4. the first computers only do simple math formulae like addition and subtraction. 5. with a reference management software on your computer at the end of a lengthy assignment you have more than 100 links. 6. the first programmers face grueling hours of counting and calculating to get operations done.