Write the form of the underlined verb indicated in the ().
They lay down their troubles for a while. (past)
"Is the past tense of lay, laid or lain?"
The past tense of lay is laid.
Check this site for an explanation.
http://www.chompchomp.com/rules/irregularrules02.htm
Look up confusable words here:
http://grammar.ccc.commnet.edu/grammar/notorious.htm
and
http://grammar.ccc.commnet.edu/grammar/notorious2.htm
Look up words alphabetically. The P's for example are in the second link; the L's are in the first link.