which of these would be fully deductible in 2021 on schedule a (form 1040), itemized deductions? investment interest expense of $800 with investment income of $900. investment interest expense of $1,200 with investment income of $1,100. investment interest expense of $1,900 with $1,350 in investment income. investment interest expense of $1,400 with investment income of $1,500 ($300 of which was from municipal bond interest).