q('<TABLE width="100%">');
q('<TR><TD ID="a16" TITLE="couldn`t find#could not<P>the answer is in the <EM>past simple</EM> for actions that happened in the past.</P>" width="5%"></TD><TD ID="def16" onClick="defClick(16);">Sorry I\'m late. I ....... find my car keys. <SPAN CLASS=prompt>(not | can)</SPAN></TD><TD align="right">~couldn\'t find#could not~</TD></TR>');
q('<TR><TD ID="a17" TITLE="haven`t been able to#have not been able to<P>the answer is in the <EM>present perfect</EM> for expressions of unfinished time.</P>" width="5%"></TD><TD ID="def17" onClick="defClick(17);">I ....... play tennis since I injured my shoulder last year. <SPAN CLASS=prompt>(not | can)</SPAN></TD><TD align="right">~haven\'t been able to#have not been able to~</TD></TR>');
q('<TR><TD ID="a18" TITLE="didn`t have to#did not have to<P>the answer is in the <EM>past simple</EM> for actions that happened in the past.</P>" width="5%"></TD><TD ID="def18" onClick="defClick(18);">I was lucky; I ....... do any homework last week, because our teacher was away! <SPAN CLASS=prompt>(not | must)</SPAN></TD><TD align="right">~didn\'t have to#did not have to~</TD></TR>');
q('<TR><TD ID="a19" TITLE="haven`t had to#have not had to<P>the answer is in the <EM>present perfect</EM> for expressions of unfinished time.</P>" width="5%"></TD><TD ID="def19" onClick="defClick(19);">Since our teacher has been away, we ....... do any homework! <SPAN CLASS=prompt>(not | must)</SPAN></TD><TD align="right">~haven\'t had to#have not had to~</TD></TR>');
q('<TR><TD ID="a20" TITLE="haven`t washed#have not washed<P>the answer is in the <EM>present perfect</EM> for expressions of unfinished time.</P>" width="5%"></TD><TD ID="def20" onClick="defClick(20);">Your car is very dirty! - I know, I ....... it since we came back from holiday. <SPAN CLASS=prompt>(not | wash)</SPAN></TD><TD align="right">~haven\'t washed#have not washed~</TD></TR>');
q('</TABLE>');