Of course I’d recommend my books, The Unofficial Answer Guide (explanations for every single answer on 6 released tests) and All The Science You Need to Know (quick book with detailed strategies for conquering the science section).
The Unofficial ACT Solutions Manual: Complete Solutions for Six Official ACT Practice Tests (The ACT Solutions Manual) https://www.amazon.com/dp/1690619694/ref=cm_sw_r_cp_api_glc_fabc_1394Fb2CHNGS2
All* the Science You Need to Know: *to Ace the ACT Science Section https://www.amazon.com/dp/1734055006/ref=cm_sw_r_cp_api_glc_fabc_j594FbS92A1RF
I also love Erica Meltzer’s English book and the Khan Academy videos.